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[PATCH v6 00/12] Support non-lru page migration

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  [PATCH v6 00/12] Support non-lru page migration Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 03/12] mm: balloon: use general non-lru movable page feature Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
      Re: [PATCH v6 03/12] mm: balloon: use general non-lru movable page  feature Vlastimil Babka <vbabka@suse.cz> - 2016-05-30 14:20 +0200
    [PATCH v6 12/12] zram: use __GFP_MOVABLE for memory allocation Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 05/12] zsmalloc: use bit_spin_lock Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
      Re: [PATCH v6 11/12] zsmalloc: page migration support Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-05-24 07:30 +0200
        Re: [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-24 08:30 +0200
          Re: [PATCH v6 11/12] zsmalloc: page migration support Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-05-24 10:10 +0200
            Re: [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-24 10:20 +0200
          Re: [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-25 07:20 +0200
            Re: [PATCH v6 11/12] zsmalloc: page migration support Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-05-25 16:30 +0200
              Re: [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-26 02:40 +0200
                Re: [PATCH v6 11/12] zsmalloc: page migration support Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-05-26 03:00 +0200
                  Re: [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-26 06:40 +0200
      [PATCH v6r2 11/12] zsmalloc: page migration support Minchan Kim <minchan@kernel.org> - 2016-05-27 00:00 +0200
    [PATCH v6 08/12] zsmalloc: introduce zspage structure Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 06/12] zsmalloc: use accessor Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 02/12] mm: migrate: support non-lru movable page migration Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
      Re: [PATCH v6 02/12] mm: migrate: support non-lru movable page  migration Vlastimil Babka <vbabka@suse.cz> - 2016-05-27 16:30 +0200
        Re: [PATCH v6 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-05-30 03:40 +0200
          Re: [PATCH v6 02/12] mm: migrate: support non-lru movable page  migration Vlastimil Babka <vbabka@suse.cz> - 2016-05-30 11:10 +0200
      PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration Minchan Kim <minchan@kernel.org> - 2016-05-30 03:40 +0200
        Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page  migration Vlastimil Babka <vbabka@suse.cz> - 2016-05-30 11:40 +0200
          Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-05-30 18:30 +0200
            Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page  migration Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 10:00 +0200
        [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-05-31 02:10 +0200
          Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 10:00 +0200
            Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-06-01 01:10 +0200
    [PATCH v6 10/12] zsmalloc: use freeobj for index Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 09/12] zsmalloc: separate free_zspage from putback_zspage Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 04/12] zsmalloc: keep max_object in size_class Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 01/12] mm: use put_page to free page instead of putback_lru_page Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200
    [PATCH v6 07/12] zsmalloc: factor page chain functionality out Minchan Kim <minchan@kernel.org> - 2016-05-20 16:30 +0200

Page 2 of 2 — ← Prev page 1 [2]

#1408703 — Re: [PATCH v6 02/12] mm: migrate: support non-lru movable page migration

On Fri, May 27, 2016 at 04:26:21PM +0200, Vlastimil Babka wrote:
> On 05/20/2016 04:23 PM, Minchan Kim wrote:
> >We have allowed migration for only LRU pages until now and it was
> >enough to make high-order pages. But recently, embedded system(e.g.,
> >webOS, android) uses lots of non-movable pages(e.g., zram, GPU memory)
> >so we have seen several reports about troubles of small high-order
> >allocation. For fixing the problem, there were several efforts
> >(e,g,. enhance compaction algorithm, SLUB fallback to 0-order page,
> >reserved memory, vmalloc and so on) but if there are lots of
> >non-movable pages in system, their solutions are void in the long run.
> >
> >So, this patch is to support facility to change non-movable pages
> >with movable. For the feature, this patch introduces functions related
> >to migration to address_space_operations as well as some page flags.
> >
> >If a driver want to make own pages movable, it should define three functions
> >which are function pointers of struct address_space_operations.
> >
> >1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);
> >
> >What VM expects on isolate_page function of driver is to return *true*
> >if driver isolates page successfully. On returing true, VM marks the page
> >as PG_isolated so concurrent isolation in several CPUs skip the page
> >for isolation. If a driver cannot isolate the page, it should return *false*.
> >
> >Once page is successfully isolated, VM uses page.lru fields so driver
> >shouldn't expect to preserve values in that fields.
> >
> >2. int (*migratepage) (struct address_space *mapping,
> >		struct page *newpage, struct page *oldpage, enum migrate_mode);
> >
> >After isolation, VM calls migratepage of driver with isolated page.
> >The function of migratepage is to move content of the old page to new page
> >and set up fields of struct page newpage. Keep in mind that you should
> >clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
> >migrated the oldpage successfully and returns 0.
> >If driver cannot migrate the page at the moment, driver can return -EAGAIN.
> >On -EAGAIN, VM will retry page migration in a short time because VM interprets
> >-EAGAIN as "temporal migration failure". On returning any error except -EAGAIN,
> >VM will give up the page migration without retrying in this time.
> >
> >Driver shouldn't touch page.lru field VM using in the functions.
> >
> >3. void (*putback_page)(struct page *);
> >
> >If migration fails on isolated page, VM should return the isolated page
> >to the driver so VM calls driver's putback_page with migration failed page.
> >In this function, driver should put the isolated page back to the own data
> >structure.
> >
> >4. non-lru movable page flags
> >
> >There are two page flags for supporting non-lru movable page.
> >
> >* PG_movable
> >
> >Driver should use the below function to make page movable under page_lock.
> >
> >	void __SetPageMovable(struct page *page, struct address_space *mapping)
> >
> >It needs argument of address_space for registering migration family functions
> >which will be called by VM. Exactly speaking, PG_movable is not a real flag of
> >struct page. Rather than, VM reuses page->mapping's lower bits to represent it.
> >
> >	#define PAGE_MAPPING_MOVABLE 0x2
> >	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
> 
> Interesting, let's see how that works out...
> 
> Overal this looks much better than the last version I checked!

Thanks.

> 
> [...]
> 
> >@@ -357,29 +360,37 @@ PAGEFLAG(Idle, idle, PF_ANY)
> >  * with the PAGE_MAPPING_ANON bit set to distinguish it.  See rmap.h.
> >  *
> >  * On an anonymous page in a VM_MERGEABLE area, if CONFIG_KSM is enabled,
> >- * the PAGE_MAPPING_KSM bit may be set along with the PAGE_MAPPING_ANON bit;
> >- * and then page->mapping points, not to an anon_vma, but to a private
> >+ * the PAGE_MAPPING_MOVABLE bit may be set along with the PAGE_MAPPING_ANON
> >+ * bit; and then page->mapping points, not to an anon_vma, but to a private
> >  * structure which KSM associates with that merged page.  See ksm.h.
> >  *
> >- * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is currently never used.
> >+ * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is used for non-lru movable
> >+ * page and then page->mapping points a struct address_space.
> >  *
> >  * Please note that, confusingly, "page_mapping" refers to the inode
> >  * address_space which maps the page from disk; whereas "page_mapped"
> >  * refers to user virtual address space into which the page is mapped.
> >  */
> >-#define PAGE_MAPPING_ANON	1
> >-#define PAGE_MAPPING_KSM	2
> >-#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
> >+#define PAGE_MAPPING_ANON	0x1
> >+#define PAGE_MAPPING_MOVABLE	0x2
> >+#define PAGE_MAPPING_KSM	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
> >+#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
> >
> >-static __always_inline int PageAnonHead(struct page *page)
> >+static __always_inline int PageMappingFlag(struct page *page)
> 
> PageMappingFlags()?

Yeb.

> 
> [...]
> 
> >diff --git a/mm/compaction.c b/mm/compaction.c
> >index 1427366ad673..2d6862d0df60 100644
> >--- a/mm/compaction.c
> >+++ b/mm/compaction.c
> >@@ -81,6 +81,41 @@ static inline bool migrate_async_suitable(int migratetype)
> >
> > #ifdef CONFIG_COMPACTION
> >
> >+int PageMovable(struct page *page)
> >+{
> >+	struct address_space *mapping;
> >+
> >+	WARN_ON(!PageLocked(page));
> 
> Why not VM_BUG_ON_PAGE as elsewhere?

I have backported this patchset to huge old kernel which doesn't have
VM_BUG_ON_PAGE and forgot to correct it beforre sending mainline.

Thanks.

> 
> >+	if (!__PageMovable(page))
> >+		goto out;
> 
> Just return 0.

Maybe I love goto. You realized me. I will split up will her.

> 
> >+
> >+	mapping = page_mapping(page);
> >+	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
> >+		return 1;
> >+out:
> >+	return 0;
> >+}
> >+EXPORT_SYMBOL(PageMovable);
> >+
> >+void __SetPageMovable(struct page *page, struct address_space *mapping)
> >+{
> >+	VM_BUG_ON_PAGE(!PageLocked(page), page);
> >+	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
> >+	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
> >+}
> >+EXPORT_SYMBOL(__SetPageMovable);
> >+
> >+void __ClearPageMovable(struct page *page)
> >+{
> >+	VM_BUG_ON_PAGE(!PageLocked(page), page);
> >+	VM_BUG_ON_PAGE(!PageMovable(page), page);
> >+	VM_BUG_ON_PAGE(!((unsigned long)page->mapping & PAGE_MAPPING_MOVABLE),
> >+				page);
> 
> The last line sounds redundant, PageMovable() already checked this
> via __PageMovable()

Yeb.

> 
> 
> >+	page->mapping = (void *)((unsigned long)page->mapping &
> >+				PAGE_MAPPING_MOVABLE);
> 
> This should be negated to clear... use ~PAGE_MAPPING_MOVABLE ?

No.

The intention is to clear only mapping value but PAGE_MAPPING_MOVABLE
flag. So, any new migration trial will be failed because PageMovable
checks page's mapping value but ongoing migraion handling can catch
whether it's movable page or not with the type bit.

For example, we need to keep the type bit to handle putback the page.
With parallel freeing(e.g., __ClearPageMovable) from the owner after
isolating the page, migration will be failed and put it back. Then,
we need to identify movable to clear PG_isolate and shouldn't call
mapping->a_ops->putback_page. For that, we need to keep the type bit
until the page is return to buddy.

> 
> >+}
> >+EXPORT_SYMBOL(__ClearPageMovable);
> >+
> > /* Do not skip compaction more than 64 times */
> > #define COMPACT_MAX_DEFER_SHIFT 6
> >
> >@@ -735,21 +770,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > 		}
> >
> > 		/*
> >-		 * Check may be lockless but that's ok as we recheck later.
> >-		 * It's possible to migrate LRU pages and balloon pages
> >-		 * Skip any other type of page
> >-		 */
> >-		is_lru = PageLRU(page);
> >-		if (!is_lru) {
> >-			if (unlikely(balloon_page_movable(page))) {
> >-				if (balloon_page_isolate(page)) {
> >-					/* Successfully isolated */
> >-					goto isolate_success;
> >-				}
> >-			}
> >-		}
> 
> So this effectively prevents movable compound pages from being
> migrated. Are you sure no users of this functionality are going to
> have compound pages? I assumed that they could, and so made the code
> like this, with the is_lru variable (which is redundant after your
> change).

This implementation at the moment disables effectively non-lru compound
page migration but I'm not a god so I can't make sure no one doesn't want
it in future. If someone want it, we can support it then because this work
doesn't prevent it by design.

> 
> >-		/*
> > 		 * Regardless of being on LRU, compound pages such as THP and
> > 		 * hugetlbfs are not to be compacted. We can potentially save
> > 		 * a lot of iterations if we skip them at once. The check is
> >@@ -765,8 +785,38 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > 			goto isolate_fail;
> > 		}
> >
> >-		if (!is_lru)
> >+		/*
> >+		 * Check may be lockless but that's ok as we recheck later.
> >+		 * It's possible to migrate LRU and non-lru movable pages.
> >+		 * Skip any other type of page
> >+		 */
> >+		is_lru = PageLRU(page);
> >+		if (!is_lru) {
> >+			if (unlikely(balloon_page_movable(page))) {
> >+				if (balloon_page_isolate(page)) {
> >+					/* Successfully isolated */
> >+					goto isolate_success;
> >+				}
> >+			}
> 
> [...]
> 
> >+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
> >+{
> >+	struct address_space *mapping;
> >+
> >+	/*
> >+	 * Avoid burning cycles with pages that are yet under __free_pages(),
> >+	 * or just got freed under us.
> >+	 *
> >+	 * In case we 'win' a race for a movable page being freed under us and
> >+	 * raise its refcount preventing __free_pages() from doing its job
> >+	 * the put_page() at the end of this block will take care of
> >+	 * release this page, thus avoiding a nasty leakage.
> >+	 */
> >+	if (unlikely(!get_page_unless_zero(page)))
> >+		goto out;
> >+
> >+	/*
> >+	 * Check PageMovable before holding a PG_lock because page's owner
> >+	 * assumes anybody doesn't touch PG_lock of newly allocated page
> >+	 * so unconditionally grapping the lock ruins page's owner side.
> >+	 */
> >+	if (unlikely(!__PageMovable(page)))
> >+		goto out_putpage;
> >+	/*
> >+	 * As movable pages are not isolated from LRU lists, concurrent
> >+	 * compaction threads can race against page migration functions
> >+	 * as well as race against the releasing a page.
> >+	 *
> >+	 * In order to avoid having an already isolated movable page
> >+	 * being (wrongly) re-isolated while it is under migration,
> >+	 * or to avoid attempting to isolate pages being released,
> >+	 * lets be sure we have the page lock
> >+	 * before proceeding with the movable page isolation steps.
> >+	 */
> >+	if (unlikely(!trylock_page(page)))
> >+		goto out_putpage;
> >+
> >+	if (!PageMovable(page) || PageIsolated(page))
> >+		goto out_no_isolated;
> >+
> >+	mapping = page_mapping(page);
> 
> Hmm so on first tail page of a THP compound page, page->mapping will
> alias with compound_mapcount. That can easily have a value matching
> PageMovable flags and we'll proceed and start inspecting the
> compound head in page_mapping()... maybe it's not a big deal, or we
> better check and skip PageTail first, must think about it more...

I thouht PageCompound check right before isolate_movable_page in
isolate_migratepages_block will filter it out mostly but yeah
it is racy without zone->lru_lock so it could reach to isolate_movable_page.
However, PageMovable check in there investigates mapping, mapping->a_ops,
and a_ops->isolate_page to verify whether it's movable page or not.

I thought it's sufficient to filter THP page.

> 
> [...]
> 
> >@@ -755,33 +844,69 @@ static int move_to_new_page(struct page *newpage, struct page *page,
> > 				enum migrate_mode mode)
> > {
> > 	struct address_space *mapping;
> >-	int rc;
> >+	int rc = -EAGAIN;
> >+	bool is_lru = !__PageMovable(page);
> >
> > 	VM_BUG_ON_PAGE(!PageLocked(page), page);
> > 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
> >
> > 	mapping = page_mapping(page);
> >-	if (!mapping)
> >-		rc = migrate_page(mapping, newpage, page, mode);
> >-	else if (mapping->a_ops->migratepage)
> >-		/*
> >-		 * Most pages have a mapping and most filesystems provide a
> >-		 * migratepage callback. Anonymous pages are part of swap
> >-		 * space which also has its own migratepage callback. This
> >-		 * is the most common path for page migration.
> >-		 */
> >-		rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
> >-	else
> >-		rc = fallback_migrate_page(mapping, newpage, page, mode);
> >+	/*
> >+	 * In case of non-lru page, it could be released after
> >+	 * isolation step. In that case, we shouldn't try
> >+	 * fallback migration which is designed for LRU pages.
> >+	 */
> 
> Hmm but is_lru was determined from !__PageMovable() above, also well
> after the isolation step. So if the driver already released it, we
> wouldn't detect it? And this function is all under same page lock,
> so if __PageMovable was true above, so will be PageMovable below?

You are missing what I mentioned above.
We should keep the type bit to catch what you are saying(i.e., driver
already released).

__PageMovable just checks PAGE_MAPPING_MOVABLE flag and PageMovable
checks page->mapping valid while __ClearPageMovable reset only
valid vaule of mapping, not PAGE_MAPPING_MOVABLE flag.

I wrote it down in Documentation/vm/page_migration.

"For testing of non-lru movable page, VM supports __PageMovable function.
However, it doesn't guarantee to identify non-lru movable page because
page->mapping field is unified with other variables in struct page.
As well, if driver releases the page after isolation by VM, page->mapping
doesn't have stable value although it has PAGE_MAPPING_MOVABLE
(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
page is LRU or non-lru movable once the page has been isolated. Because
LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
good for just peeking to test non-lru movable pages before more expensive
checking with lock_page in pfn scanning to select victim.

For guaranteeing non-lru movable page, VM provides PageMovable function.
Unlike __PageMovable, PageMovable functions validates page->mapping and 
mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
destroying of page->mapping.

Driver using __SetPageMovable should clear the flag via __ClearMovablePage
under page_lock before the releasing the page."

> 
> >+	if (unlikely(!is_lru)) {
> >+		VM_BUG_ON_PAGE(!PageIsolated(page), page);
> >+		if (!PageMovable(page)) {
> >+			rc = MIGRATEPAGE_SUCCESS;
> >+			__ClearPageIsolated(page);
> >+			goto out;
> >+		}
> >+	}
> >+
> >+	if (likely(is_lru)) {
> >+		if (!mapping)
> >+			rc = migrate_page(mapping, newpage, page, mode);
> >+		else if (mapping->a_ops->migratepage)
> >+			/*
> >+			 * Most pages have a mapping and most filesystems
> >+			 * provide a migratepage callback. Anonymous pages
> >+			 * are part of swap space which also has its own
> >+			 * migratepage callback. This is the most common path
> >+			 * for page migration.
> >+			 */
> >+			rc = mapping->a_ops->migratepage(mapping, newpage,
> >+							page, mode);
> >+		else
> >+			rc = fallback_migrate_page(mapping, newpage,
> >+							page, mode);
> >+	} else {
> >+		rc = mapping->a_ops->migratepage(mapping, newpage,
> >+						page, mode);
> >+		WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
> >+			!PageIsolated(page));
> >+	}
> 
> Why split the !is_lru handling in two places?

Fixed.

> 
> >
> > 	/*
> > 	 * When successful, old pagecache page->mapping must be cleared before
> > 	 * page is freed; but stats require that PageAnon be left as PageAnon.
> > 	 */
> > 	if (rc == MIGRATEPAGE_SUCCESS) {
> >-		if (!PageAnon(page))
> >+		if (__PageMovable(page)) {
> >+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
> >+
> >+			/*
> >+			 * We clear PG_movable under page_lock so any compactor
> >+			 * cannot try to migrate this page.
> >+			 */
> >+			__ClearPageIsolated(page);
> >+		}
> >+
> >+		if (!((unsigned long)page->mapping & PAGE_MAPPING_FLAGS))
> > 			page->mapping = NULL;
> 
> The two lines above make little sense to me without a comment.

I folded this.

@@ -901,7 +901,12 @@ static int move_to_new_page(struct page *newpage, struct page *page,
                        __ClearPageIsolated(page);
                }
 
-               if (!((unsigned long)page->mapping & PAGE_MAPPING_FLAGS))
+               /*
+                * Anonymous and movable page->mapping will be cleard by
+                * free_pages_prepare so don't reset it here for keeping
+                * the type to work PageAnon, for example.
+                */
+               if (!PageMappingFlags(page))
                        page->mapping = NULL;
        }
 out:


> Should the condition be negated, even?

No.

> 
> 

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#1408905 — Re: [PATCH v6 02/12] mm: migrate: support non-lru movable page migration

On 05/30/2016 03:33 AM, Minchan Kim wrote:
>>
>>
>>> +	page->mapping = (void *)((unsigned long)page->mapping &
>>> +				PAGE_MAPPING_MOVABLE);
>>
>> This should be negated to clear... use ~PAGE_MAPPING_MOVABLE ?
>
> No.
>
> The intention is to clear only mapping value but PAGE_MAPPING_MOVABLE
> flag. So, any new migration trial will be failed because PageMovable
> checks page's mapping value but ongoing migraion handling can catch
> whether it's movable page or not with the type bit.

Oh, OK, I got that wrong. I'll point out in the reply to the v6v2 what 
misled me :)

>>
>> So this effectively prevents movable compound pages from being
>> migrated. Are you sure no users of this functionality are going to
>> have compound pages? I assumed that they could, and so made the code
>> like this, with the is_lru variable (which is redundant after your
>> change).
>
> This implementation at the moment disables effectively non-lru compound
> page migration but I'm not a god so I can't make sure no one doesn't want
> it in future. If someone want it, we can support it then because this work
> doesn't prevent it by design.

Oh well. As long as the balloon pages or zsmalloc don't already use 
compound pages...

>
> I thouht PageCompound check right before isolate_movable_page in
> isolate_migratepages_block will filter it out mostly but yeah
> it is racy without zone->lru_lock so it could reach to isolate_movable_page.
> However, PageMovable check in there investigates mapping, mapping->a_ops,
> and a_ops->isolate_page to verify whether it's movable page or not.
>
> I thought it's sufficient to filter THP page.

I guess, yeah.

>>
>> [...]
>>
>>> @@ -755,33 +844,69 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>>> 				enum migrate_mode mode)
>>> {
>>> 	struct address_space *mapping;
>>> -	int rc;
>>> +	int rc = -EAGAIN;
>>> +	bool is_lru = !__PageMovable(page);
>>>
>>> 	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
>>>
>>> 	mapping = page_mapping(page);
>>> -	if (!mapping)
>>> -		rc = migrate_page(mapping, newpage, page, mode);
>>> -	else if (mapping->a_ops->migratepage)
>>> -		/*
>>> -		 * Most pages have a mapping and most filesystems provide a
>>> -		 * migratepage callback. Anonymous pages are part of swap
>>> -		 * space which also has its own migratepage callback. This
>>> -		 * is the most common path for page migration.
>>> -		 */
>>> -		rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
>>> -	else
>>> -		rc = fallback_migrate_page(mapping, newpage, page, mode);
>>> +	/*
>>> +	 * In case of non-lru page, it could be released after
>>> +	 * isolation step. In that case, we shouldn't try
>>> +	 * fallback migration which is designed for LRU pages.
>>> +	 */
>>
>> Hmm but is_lru was determined from !__PageMovable() above, also well
>> after the isolation step. So if the driver already released it, we
>> wouldn't detect it? And this function is all under same page lock,
>> so if __PageMovable was true above, so will be PageMovable below?
>
> You are missing what I mentioned above.
> We should keep the type bit to catch what you are saying(i.e., driver
> already released).
>
> __PageMovable just checks PAGE_MAPPING_MOVABLE flag and PageMovable
> checks page->mapping valid while __ClearPageMovable reset only
> valid vaule of mapping, not PAGE_MAPPING_MOVABLE flag.
>
> I wrote it down in Documentation/vm/page_migration.
>
> "For testing of non-lru movable page, VM supports __PageMovable function.
> However, it doesn't guarantee to identify non-lru movable page because
> page->mapping field is unified with other variables in struct page.
> As well, if driver releases the page after isolation by VM, page->mapping
> doesn't have stable value although it has PAGE_MAPPING_MOVABLE
> (Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
> page is LRU or non-lru movable once the page has been isolated. Because
> LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
> good for just peeking to test non-lru movable pages before more expensive
> checking with lock_page in pfn scanning to select victim.
>
> For guaranteeing non-lru movable page, VM provides PageMovable function.
> Unlike __PageMovable, PageMovable functions validates page->mapping and
> mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
> destroying of page->mapping.
>
> Driver using __SetPageMovable should clear the flag via __ClearMovablePage
> under page_lock before the releasing the page."

Right, I get it now.


>>> +		if (!((unsigned long)page->mapping & PAGE_MAPPING_FLAGS))
>>> 			page->mapping = NULL;
>>
>> The two lines above make little sense to me without a comment.
>
> I folded this.
>
> @@ -901,7 +901,12 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>                         __ClearPageIsolated(page);
>                 }
>
> -               if (!((unsigned long)page->mapping & PAGE_MAPPING_FLAGS))
> +               /*
> +                * Anonymous and movable page->mapping will be cleard by
> +                * free_pages_prepare so don't reset it here for keeping
> +                * the type to work PageAnon, for example.
> +                */
> +               if (!PageMappingFlags(page))
>                         page->mapping = NULL;
>         }

Thanks.

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#1408702 — PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration

Per Vlastimil's review comment,

Vlastimil, I updated based on your comment. Please review this.
If everything is done, I will send v7 rebased on recent mmotm.

Thanks for the review!

From ad4157e98651a2d18fd0a4ae90d1d9f609aab314 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 8 Apr 2016 10:34:49 +0900
Subject: [PATCH v6r2] mm: migrate: support non-lru movable page migration

We have allowed migration for only LRU pages until now and it was
enough to make high-order pages. But recently, embedded system(e.g.,
webOS, android) uses lots of non-movable pages(e.g., zram, GPU memory)
so we have seen several reports about troubles of small high-order
allocation. For fixing the problem, there were several efforts
(e,g,. enhance compaction algorithm, SLUB fallback to 0-order page,
reserved memory, vmalloc and so on) but if there are lots of
non-movable pages in system, their solutions are void in the long run.

So, this patch is to support facility to change non-movable pages
with movable. For the feature, this patch introduces functions related
to migration to address_space_operations as well as some page flags.

If a driver want to make own pages movable, it should define three functions
which are function pointers of struct address_space_operations.

1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);

What VM expects on isolate_page function of driver is to return *true*
if driver isolates page successfully. On returing true, VM marks the page
as PG_isolated so concurrent isolation in several CPUs skip the page
for isolation. If a driver cannot isolate the page, it should return *false*.

Once page is successfully isolated, VM uses page.lru fields so driver
shouldn't expect to preserve values in that fields.

2. int (*migratepage) (struct address_space *mapping,
		struct page *newpage, struct page *oldpage, enum migrate_mode);

After isolation, VM calls migratepage of driver with isolated page.
The function of migratepage is to move content of the old page to new page
and set up fields of struct page newpage. Keep in mind that you should
clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
migrated the oldpage successfully and returns 0.
If driver cannot migrate the page at the moment, driver can return -EAGAIN.
On -EAGAIN, VM will retry page migration in a short time because VM interprets
-EAGAIN as "temporal migration failure". On returning any error except -EAGAIN,
VM will give up the page migration without retrying in this time.

Driver shouldn't touch page.lru field VM using in the functions.

3. void (*putback_page)(struct page *);

If migration fails on isolated page, VM should return the isolated page
to the driver so VM calls driver's putback_page with migration failed page.
In this function, driver should put the isolated page back to the own data
structure.

4. non-lru movable page flags

There are two page flags for supporting non-lru movable page.

* PG_movable

Driver should use the below function to make page movable under page_lock.

	void __SetPageMovable(struct page *page, struct address_space *mapping)

It needs argument of address_space for registering migration family functions
which will be called by VM. Exactly speaking, PG_movable is not a real flag of
struct page. Rather than, VM reuses page->mapping's lower bits to represent it.

	#define PAGE_MAPPING_MOVABLE 0x2
	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;

so driver shouldn't access page->mapping directly. Instead, driver should
use page_mapping which mask off the low two bits of page->mapping so it can get
right struct address_space.

For testing of non-lru movable page, VM supports __PageMovable function.
However, it doesn't guarantee to identify non-lru movable page because
page->mapping field is unified with other variables in struct page.
As well, if driver releases the page after isolation by VM, page->mapping
doesn't have stable value although it has PAGE_MAPPING_MOVABLE
(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
page is LRU or non-lru movable once the page has been isolated. Because
LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
good for just peeking to test non-lru movable pages before more expensive
checking with lock_page in pfn scanning to select victim.

For guaranteeing non-lru movable page, VM provides PageMovable function.
Unlike __PageMovable, PageMovable functions validates page->mapping and
mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
destroying of page->mapping.

Driver using __SetPageMovable should clear the flag via __ClearMovablePage
under page_lock before the releasing the page.

* PG_isolated

To prevent concurrent isolation among several CPUs, VM marks isolated page
as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
movable page, it can skip it. Driver doesn't need to manipulate the flag
because VM will set/clear it automatically. Keep in mind that if driver
sees PG_isolated page, it means the page have been isolated by VM so it
shouldn't touch page.lru field.
PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
for own purpose.

Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: John Einar Reitan <john.reitan@foss.arm.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 Documentation/filesystems/Locking |   4 +
 Documentation/filesystems/vfs.txt |  11 +++
 Documentation/vm/page_migration   | 107 ++++++++++++++++++++-
 include/linux/compaction.h        |  17 ++++
 include/linux/fs.h                |   2 +
 include/linux/ksm.h               |   3 +-
 include/linux/migrate.h           |   2 +
 include/linux/mm.h                |   1 +
 include/linux/page-flags.h        |  33 +++++--
 mm/compaction.c                   |  80 ++++++++++++----
 mm/ksm.c                          |   4 +-
 mm/migrate.c                      | 192 ++++++++++++++++++++++++++++++++++----
 mm/page_alloc.c                   |   2 +-
 mm/util.c                         |   6 +-
 14 files changed, 412 insertions(+), 52 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index af7c030a0368..3991a976cf43 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -195,7 +195,9 @@ unlocks and drops the reference.
 	int (*releasepage) (struct page *, int);
 	void (*freepage)(struct page *);
 	int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
+	bool (*isolate_page) (struct page *, isolate_mode_t);
 	int (*migratepage)(struct address_space *, struct page *, struct page *);
+	void (*putback_page) (struct page *);
 	int (*launder_page)(struct page *);
 	int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
 	int (*error_remove_page)(struct address_space *, struct page *);
@@ -219,7 +221,9 @@ invalidatepage:		yes
 releasepage:		yes
 freepage:		yes
 direct_IO:
+isolate_page:		yes
 migratepage:		yes (both)
+putback_page:		yes
 launder_page:		yes
 is_partially_uptodate:	yes
 error_remove_page:	yes
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 19366fef2652..9d4ae317fdcb 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -591,9 +591,14 @@ struct address_space_operations {
 	int (*releasepage) (struct page *, int);
 	void (*freepage)(struct page *);
 	ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);
+	/* isolate a page for migration */
+	bool (*isolate_page) (struct page *, isolate_mode_t);
 	/* migrate the contents of a page to the specified target */
 	int (*migratepage) (struct page *, struct page *);
+	/* put migration-failed page back to right list */
+	void (*putback_page) (struct page *);
 	int (*launder_page) (struct page *);
+
 	int (*is_partially_uptodate) (struct page *, unsigned long,
 					unsigned long);
 	void (*is_dirty_writeback) (struct page *, bool *, bool *);
@@ -739,6 +744,10 @@ struct address_space_operations {
         and transfer data directly between the storage and the
         application's address space.
 
+  isolate_page: Called by the VM when isolating a movable non-lru page.
+	If page is successfully isolated, VM marks the page as PG_isolated
+	via __SetPageIsolated.
+
   migrate_page:  This is used to compact the physical memory usage.
         If the VM wants to relocate a page (maybe off a memory card
         that is signalling imminent failure) it will pass a new page
@@ -746,6 +755,8 @@ struct address_space_operations {
 	transfer any private data across and update any references
         that it has to the page.
 
+  putback_page: Called by the VM when isolated page's migration fails.
+
   launder_page: Called before freeing a page - it writes back the dirty page. To
   	prevent redirtying the page, it is kept locked during the whole
 	operation.
diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
index fea5c0864170..80e98af46e95 100644
--- a/Documentation/vm/page_migration
+++ b/Documentation/vm/page_migration
@@ -142,5 +142,110 @@ is increased so that the page cannot be freed while page migration occurs.
 20. The new page is moved to the LRU and can be scanned by the swapper
     etc again.
 
-Christoph Lameter, May 8, 2006.
+C. Non-LRU page migration
+-------------------------
+
+Although original migration aimed for reducing the latency of memory access
+for NUMA, compaction who want to create high-order page is also main customer.
+
+Current problem of the implementation is that it is designed to migrate only
+*LRU* pages. However, there are potential non-lru pages which can be migrated
+in drivers, for example, zsmalloc, virtio-balloon pages.
+
+For virtio-balloon pages, some parts of migration code path have been hooked
+up and added virtio-balloon specific functions to intercept migration logics.
+It's too specific to a driver so other drivers who want to make their pages
+movable would have to add own specific hooks in migration path.
+
+To overclome the problem, VM supports non-LRU page migration which provides
+generic functions for non-LRU movable pages without driver specific hooks
+migration path.
+
+If a driver want to make own pages movable, it should define three functions
+which are function pointers of struct address_space_operations.
+
+1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);
+
+What VM expects on isolate_page function of driver is to return *true*
+if driver isolates page successfully. On returing true, VM marks the page
+as PG_isolated so concurrent isolation in several CPUs skip the page
+for isolation. If a driver cannot isolate the page, it should return *false*.
+
+Once page is successfully isolated, VM uses page.lru fields so driver
+shouldn't expect to preserve values in that fields.
+
+2. int (*migratepage) (struct address_space *mapping,
+		struct page *newpage, struct page *oldpage, enum migrate_mode);
+
+After isolation, VM calls migratepage of driver with isolated page.
+The function of migratepage is to move content of the old page to new page
+and set up fields of struct page newpage. Keep in mind that you should
+clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
+migrated the oldpage successfully and returns 0.
+If driver cannot migrate the page at the moment, driver can return -EAGAIN.
+On -EAGAIN, VM will retry page migration in a short time because VM interprets
+-EAGAIN as "temporal migration failure". On returning any error except -EAGAIN,
+VM will give up the page migration without retrying in this time.
+
+Driver shouldn't touch page.lru field VM using in the functions.
+
+3. void (*putback_page)(struct page *);
+
+If migration fails on isolated page, VM should return the isolated page
+to the driver so VM calls driver's putback_page with migration failed page.
+In this function, driver should put the isolated page back to the own data
+structure.
 
+4. non-lru movable page flags
+
+There are two page flags for supporting non-lru movable page.
+
+* PG_movable
+
+Driver should use the below function to make page movable under page_lock.
+
+	void __SetPageMovable(struct page *page, struct address_space *mapping)
+
+It needs argument of address_space for registering migration family functions
+which will be called by VM. Exactly speaking, PG_movable is not a real flag of
+struct page. Rather than, VM reuses page->mapping's lower bits to represent it.
+
+	#define PAGE_MAPPING_MOVABLE 0x2
+	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
+
+so driver shouldn't access page->mapping directly. Instead, driver should
+use page_mapping which mask off the low two bits of page->mapping so it can get
+right struct address_space.
+
+For testing of non-lru movable page, VM supports __PageMovable function.
+However, it doesn't guarantee to identify non-lru movable page because
+page->mapping field is unified with other variables in struct page.
+As well, if driver releases the page after isolation by VM, page->mapping
+doesn't have stable value although it has PAGE_MAPPING_MOVABLE
+(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
+page is LRU or non-lru movable once the page has been isolated. Because
+LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
+good for just peeking to test non-lru movable pages before more expensive
+checking with lock_page in pfn scanning to select victim.
+
+For guaranteeing non-lru movable page, VM provides PageMovable function.
+Unlike __PageMovable, PageMovable functions validates page->mapping and
+mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
+destroying of page->mapping.
+
+Driver using __SetPageMovable should clear the flag via __ClearMovablePage
+under page_lock before the releasing the page.
+
+* PG_isolated
+
+To prevent concurrent isolation among several CPUs, VM marks isolated page
+as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
+movable page, it can skip it. Driver doesn't need to manipulate the flag
+because VM will set/clear it automatically. Keep in mind that if driver
+sees PG_isolated page, it means the page have been isolated by VM so it
+shouldn't touch page.lru field.
+PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
+for own purpose.
+
+Christoph Lameter, May 8, 2006.
+Minchan Kim, Mar 28, 2016.
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index a58c852a268f..c6b47c861cea 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -54,6 +54,9 @@ enum compact_result {
 struct alloc_context; /* in mm/internal.h */
 
 #ifdef CONFIG_COMPACTION
+extern int PageMovable(struct page *page);
+extern void __SetPageMovable(struct page *page, struct address_space *mapping);
+extern void __ClearPageMovable(struct page *page);
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
 			void __user *buffer, size_t *length, loff_t *ppos);
@@ -151,6 +154,19 @@ extern void kcompactd_stop(int nid);
 extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx);
 
 #else
+static inline int PageMovable(struct page *page)
+{
+	return 0;
+}
+static inline void __SetPageMovable(struct page *page,
+			struct address_space *mapping)
+{
+}
+
+static inline void __ClearPageMovable(struct page *page)
+{
+}
+
 static inline enum compact_result try_to_compact_pages(gfp_t gfp_mask,
 			unsigned int order, int alloc_flags,
 			const struct alloc_context *ac,
@@ -212,6 +228,7 @@ static inline void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_i
 #endif /* CONFIG_COMPACTION */
 
 #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
+struct node;
 extern int compaction_register_node(struct node *node);
 extern void compaction_unregister_node(struct node *node);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0cfdf2aec8f7..39ef97414033 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -402,6 +402,8 @@ struct address_space_operations {
 	 */
 	int (*migratepage) (struct address_space *,
 			struct page *, struct page *, enum migrate_mode);
+	bool (*isolate_page)(struct page *, isolate_mode_t);
+	void (*putback_page)(struct page *);
 	int (*launder_page) (struct page *);
 	int (*is_partially_uptodate) (struct page *, unsigned long,
 					unsigned long);
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7ae216a39c9e..481c8c4627ca 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -43,8 +43,7 @@ static inline struct stable_node *page_stable_node(struct page *page)
 static inline void set_page_stable_node(struct page *page,
 					struct stable_node *stable_node)
 {
-	page->mapping = (void *)stable_node +
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
 }
 
 /*
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 9b50325e4ddf..404fbfefeb33 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -37,6 +37,8 @@ extern int migrate_page(struct address_space *,
 			struct page *, struct page *, enum migrate_mode);
 extern int migrate_pages(struct list_head *l, new_page_t new, free_page_t free,
 		unsigned long private, enum migrate_mode mode, int reason);
+extern bool isolate_movable_page(struct page *page, isolate_mode_t mode);
+extern void putback_movable_page(struct page *page);
 
 extern int migrate_prep(void);
 extern int migrate_prep_local(void);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a00ec816233a..33eaec57e997 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1035,6 +1035,7 @@ static inline pgoff_t page_file_index(struct page *page)
 }
 
 bool page_mapped(struct page *page);
+struct address_space *page_mapping(struct page *page);
 
 /*
  * Return true only if the page has been allocated with
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e5a32445f930..f36dbb3a3060 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -129,6 +129,9 @@ enum pageflags {
 
 	/* Compound pages. Stored in first tail page's flags */
 	PG_double_map = PG_private_2,
+
+	/* non-lru isolated movable page */
+	PG_isolated = PG_reclaim,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -357,29 +360,37 @@ PAGEFLAG(Idle, idle, PF_ANY)
  * with the PAGE_MAPPING_ANON bit set to distinguish it.  See rmap.h.
  *
  * On an anonymous page in a VM_MERGEABLE area, if CONFIG_KSM is enabled,
- * the PAGE_MAPPING_KSM bit may be set along with the PAGE_MAPPING_ANON bit;
- * and then page->mapping points, not to an anon_vma, but to a private
+ * the PAGE_MAPPING_MOVABLE bit may be set along with the PAGE_MAPPING_ANON
+ * bit; and then page->mapping points, not to an anon_vma, but to a private
  * structure which KSM associates with that merged page.  See ksm.h.
  *
- * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is currently never used.
+ * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is used for non-lru movable
+ * page and then page->mapping points a struct address_space.
  *
  * Please note that, confusingly, "page_mapping" refers to the inode
  * address_space which maps the page from disk; whereas "page_mapped"
  * refers to user virtual address space into which the page is mapped.
  */
-#define PAGE_MAPPING_ANON	1
-#define PAGE_MAPPING_KSM	2
-#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
+#define PAGE_MAPPING_ANON	0x1
+#define PAGE_MAPPING_MOVABLE	0x2
+#define PAGE_MAPPING_KSM	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
+#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
 
-static __always_inline int PageAnonHead(struct page *page)
+static __always_inline int PageMappingFlags(struct page *page)
 {
-	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
+	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0;
 }
 
 static __always_inline int PageAnon(struct page *page)
 {
 	page = compound_head(page);
-	return PageAnonHead(page);
+	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
+}
+
+static __always_inline int __PageMovable(struct page *page)
+{
+	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
+				PAGE_MAPPING_MOVABLE;
 }
 
 #ifdef CONFIG_KSM
@@ -393,7 +404,7 @@ static __always_inline int PageKsm(struct page *page)
 {
 	page = compound_head(page);
 	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+				PAGE_MAPPING_KSM;
 }
 #else
 TESTPAGEFLAG_FALSE(Ksm)
@@ -641,6 +652,8 @@ static inline void __ClearPageBalloon(struct page *page)
 	atomic_set(&page->_mapcount, -1);
 }
 
+__PAGEFLAG(Isolated, isolated, PF_ANY);
+
 /*
  * If network-based swap is enabled, sl*b must keep track of whether pages
  * were allocated from pfmemalloc reserves.
diff --git a/mm/compaction.c b/mm/compaction.c
index 1427366ad673..c7e0cd4dda9d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
 
 #ifdef CONFIG_COMPACTION
 
+int PageMovable(struct page *page)
+{
+	struct address_space *mapping;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	if (!__PageMovable(page))
+		return 0;
+
+	mapping = page_mapping(page);
+	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
+		return 1;
+
+	return 0;
+}
+EXPORT_SYMBOL(PageMovable);
+
+void __SetPageMovable(struct page *page, struct address_space *mapping)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
+	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
+}
+EXPORT_SYMBOL(__SetPageMovable);
+
+void __ClearPageMovable(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	page->mapping = (void *)((unsigned long)page->mapping &
+				PAGE_MAPPING_MOVABLE);
+}
+EXPORT_SYMBOL(__ClearPageMovable);
+
 /* Do not skip compaction more than 64 times */
 #define COMPACT_MAX_DEFER_SHIFT 6
 
@@ -735,21 +768,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		}
 
 		/*
-		 * Check may be lockless but that's ok as we recheck later.
-		 * It's possible to migrate LRU pages and balloon pages
-		 * Skip any other type of page
-		 */
-		is_lru = PageLRU(page);
-		if (!is_lru) {
-			if (unlikely(balloon_page_movable(page))) {
-				if (balloon_page_isolate(page)) {
-					/* Successfully isolated */
-					goto isolate_success;
-				}
-			}
-		}
-
-		/*
 		 * Regardless of being on LRU, compound pages such as THP and
 		 * hugetlbfs are not to be compacted. We can potentially save
 		 * a lot of iterations if we skip them at once. The check is
@@ -765,8 +783,38 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			goto isolate_fail;
 		}
 
-		if (!is_lru)
+		/*
+		 * Check may be lockless but that's ok as we recheck later.
+		 * It's possible to migrate LRU and non-lru movable pages.
+		 * Skip any other type of page
+		 */
+		is_lru = PageLRU(page);
+		if (!is_lru) {
+			if (unlikely(balloon_page_movable(page))) {
+				if (balloon_page_isolate(page)) {
+					/* Successfully isolated */
+					goto isolate_success;
+				}
+			}
+
+			/*
+			 * __PageMovable can return false positive so we need
+			 * to verify it under page_lock.
+			 */
+			if (unlikely(__PageMovable(page)) &&
+					!PageIsolated(page)) {
+				if (locked) {
+					spin_unlock_irqrestore(&zone->lru_lock,
+									flags);
+					locked = false;
+				}
+
+				if (isolate_movable_page(page, isolate_mode))
+					goto isolate_success;
+			}
+
 			goto isolate_fail;
+		}
 
 		/*
 		 * Migration will fail if an anonymous page is pinned in memory,
diff --git a/mm/ksm.c b/mm/ksm.c
index 4786b4150f62..35b8aef867a9 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -532,8 +532,8 @@ static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
 	void *expected_mapping;
 	unsigned long kpfn;
 
-	expected_mapping = (void *)stable_node +
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+	expected_mapping = (void *)((unsigned long)stable_node |
+					PAGE_MAPPING_KSM);
 again:
 	kpfn = READ_ONCE(stable_node->kpfn);
 	page = pfn_to_page(kpfn);
diff --git a/mm/migrate.c b/mm/migrate.c
index 2666f28b5236..60abcf379b51 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -31,6 +31,7 @@
 #include <linux/vmalloc.h>
 #include <linux/security.h>
 #include <linux/backing-dev.h>
+#include <linux/compaction.h>
 #include <linux/syscalls.h>
 #include <linux/hugetlb.h>
 #include <linux/hugetlb_cgroup.h>
@@ -73,6 +74,81 @@ int migrate_prep_local(void)
 	return 0;
 }
 
+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+	struct address_space *mapping;
+
+	/*
+	 * Avoid burning cycles with pages that are yet under __free_pages(),
+	 * or just got freed under us.
+	 *
+	 * In case we 'win' a race for a movable page being freed under us and
+	 * raise its refcount preventing __free_pages() from doing its job
+	 * the put_page() at the end of this block will take care of
+	 * release this page, thus avoiding a nasty leakage.
+	 */
+	if (unlikely(!get_page_unless_zero(page)))
+		goto out;
+
+	/*
+	 * Check PageMovable before holding a PG_lock because page's owner
+	 * assumes anybody doesn't touch PG_lock of newly allocated page
+	 * so unconditionally grapping the lock ruins page's owner side.
+	 */
+	if (unlikely(!__PageMovable(page)))
+		goto out_putpage;
+	/*
+	 * As movable pages are not isolated from LRU lists, concurrent
+	 * compaction threads can race against page migration functions
+	 * as well as race against the releasing a page.
+	 *
+	 * In order to avoid having an already isolated movable page
+	 * being (wrongly) re-isolated while it is under migration,
+	 * or to avoid attempting to isolate pages being released,
+	 * lets be sure we have the page lock
+	 * before proceeding with the movable page isolation steps.
+	 */
+	if (unlikely(!trylock_page(page)))
+		goto out_putpage;
+
+	if (!PageMovable(page) || PageIsolated(page))
+		goto out_no_isolated;
+
+	mapping = page_mapping(page);
+	VM_BUG_ON_PAGE(!mapping, page);
+
+	if (!mapping->a_ops->isolate_page(page, mode))
+		goto out_no_isolated;
+
+	/* Driver shouldn't use PG_isolated bit of page->flags */
+	WARN_ON_ONCE(PageIsolated(page));
+	__SetPageIsolated(page);
+	unlock_page(page);
+
+	return true;
+
+out_no_isolated:
+	unlock_page(page);
+out_putpage:
+	put_page(page);
+out:
+	return false;
+}
+
+/* It should be called on page which is PG_movable */
+void putback_movable_page(struct page *page)
+{
+	struct address_space *mapping;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+	mapping = page_mapping(page);
+	mapping->a_ops->putback_page(page);
+	__ClearPageIsolated(page);
+}
+
 /*
  * Put previously isolated pages back onto the appropriate lists
  * from where they were once taken off for compaction/migration.
@@ -94,10 +170,25 @@ void putback_movable_pages(struct list_head *l)
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
-		if (unlikely(isolated_balloon_page(page)))
+		if (unlikely(isolated_balloon_page(page))) {
 			balloon_page_putback(page);
-		else
+		/*
+		 * We isolated non-lru movable page so here we can use
+		 * __PageMovable because LRU page's mapping cannot have
+		 * PAGE_MAPPING_MOVABLE.
+		 */
+		} else if (unlikely(__PageMovable(page))) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		} else {
 			putback_lru_page(page);
+		}
 	}
 }
 
@@ -592,7 +683,7 @@ void migrate_page_copy(struct page *newpage, struct page *page)
  ***********************************************************/
 
 /*
- * Common logic to directly migrate a single page suitable for
+ * Common logic to directly migrate a single LRU page suitable for
  * pages that do not use PagePrivate/PagePrivate2.
  *
  * Pages are locked upon entry and exit.
@@ -755,33 +846,72 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 				enum migrate_mode mode)
 {
 	struct address_space *mapping;
-	int rc;
+	int rc = -EAGAIN;
+	bool is_lru = !__PageMovable(page);
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
 	mapping = page_mapping(page);
-	if (!mapping)
-		rc = migrate_page(mapping, newpage, page, mode);
-	else if (mapping->a_ops->migratepage)
+
+	if (likely(is_lru)) {
+		if (!mapping)
+			rc = migrate_page(mapping, newpage, page, mode);
+		else if (mapping->a_ops->migratepage)
+			/*
+			 * Most pages have a mapping and most filesystems
+			 * provide a migratepage callback. Anonymous pages
+			 * are part of swap space which also has its own
+			 * migratepage callback. This is the most common path
+			 * for page migration.
+			 */
+			rc = mapping->a_ops->migratepage(mapping, newpage,
+							page, mode);
+		else
+			rc = fallback_migrate_page(mapping, newpage,
+							page, mode);
+	} else {
 		/*
-		 * Most pages have a mapping and most filesystems provide a
-		 * migratepage callback. Anonymous pages are part of swap
-		 * space which also has its own migratepage callback. This
-		 * is the most common path for page migration.
+		 * In case of non-lru page, it could be released after
+		 * isolation step. In that case, we shouldn't try migration.
 		 */
-		rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
-	else
-		rc = fallback_migrate_page(mapping, newpage, page, mode);
+		VM_BUG_ON_PAGE(!PageIsolated(page), page);
+		if (!PageMovable(page)) {
+			rc = MIGRATEPAGE_SUCCESS;
+			__ClearPageIsolated(page);
+			goto out;
+		}
+
+		rc = mapping->a_ops->migratepage(mapping, newpage,
+						page, mode);
+		WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
+			!PageIsolated(page));
+	}
 
 	/*
 	 * When successful, old pagecache page->mapping must be cleared before
 	 * page is freed; but stats require that PageAnon be left as PageAnon.
 	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (!PageAnon(page))
+		if (__PageMovable(page)) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+			/*
+			 * We clear PG_movable under page_lock so any compactor
+			 * cannot try to migrate this page.
+			 */
+			__ClearPageIsolated(page);
+		}
+
+		/*
+		 * Anonymous and movable page->mapping will be cleard by
+		 * free_pages_prepare so don't reset it here for keeping
+		 * the type to work PageAnon, for example.
+		 */
+		if (!PageMappingFlags(page))
 			page->mapping = NULL;
 	}
+out:
 	return rc;
 }
 
@@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	int rc = -EAGAIN;
 	int page_was_mapped = 0;
 	struct anon_vma *anon_vma = NULL;
+	bool is_lru = !__PageMovable(page);
 
 	if (!trylock_page(page)) {
 		if (!force || mode == MIGRATE_ASYNC)
@@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 		goto out_unlock_both;
 	}
 
+	if (unlikely(!is_lru)) {
+		rc = move_to_new_page(newpage, page, mode);
+		goto out_unlock_both;
+	}
+
 	/*
 	 * Corner case handling:
 	 * 1. When a new swap-cache page is read into, it is added to the LRU
@@ -920,7 +1056,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	 * list in here.
 	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (unlikely(__is_movable_balloon_page(newpage)))
+		if (unlikely(__is_movable_balloon_page(newpage) ||
+				__PageMovable(newpage)))
 			put_page(newpage);
 		else
 			putback_lru_page(newpage);
@@ -961,6 +1098,12 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		/* page was freed from under us. So we are done. */
 		ClearPageActive(page);
 		ClearPageUnevictable(page);
+		if (unlikely(__PageMovable(page))) {
+			lock_page(page);
+			if (!PageMovable(page))
+				__ClearPageIsolated(page);
+			unlock_page(page);
+		}
 		if (put_new_page)
 			put_new_page(newpage, private);
 		else
@@ -1010,8 +1153,21 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 				num_poisoned_pages_inc();
 		}
 	} else {
-		if (rc != -EAGAIN)
-			putback_lru_page(page);
+		if (rc != -EAGAIN) {
+			if (likely(!__PageMovable(page))) {
+				putback_lru_page(page);
+				goto put_new;
+			}
+
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		}
+put_new:
 		if (put_new_page)
 			put_new_page(newpage, private);
 		else
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d27e8b968ac3..4d0ba8f6cfee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1014,7 +1014,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
-	if (PageAnonHead(page))
+	if (PageMappingFlags(page))
 		page->mapping = NULL;
 	if (check_free)
 		bad += free_pages_check(page);
diff --git a/mm/util.c b/mm/util.c
index 917e0e3d0f8e..b756ee36f7f0 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
 	}
 
 	mapping = page->mapping;
-	if ((unsigned long)mapping & PAGE_MAPPING_FLAGS)
+	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
 		return NULL;
-	return mapping;
+
+	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
 }
+EXPORT_SYMBOL(page_mapping);
 
 /* Slow path of page_mapcount() for compound pages */
 int __page_mapcount(struct page *page)
-- 
1.9.1

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#1408944 — Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration

On 05/30/2016 03:39 AM, Minchan Kim wrote:
> After isolation, VM calls migratepage of driver with isolated page.
> The function of migratepage is to move content of the old page to new page
> and set up fields of struct page newpage. Keep in mind that you should
> clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
> migrated the oldpage successfully and returns 0.

This "clear PG_movable" is one of the reasons I was confused about what 
__ClearPageMovable() really does. There's no actual "PG_movable" page 
flag and the function doesn't clear even the actual mapping flag :) Also 
same thing in the Documentation/ part.

Something like "... you should indicate to the VM that the oldpage is no 
longer movable via __ClearPageMovable() ..."?

> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
>
>  #ifdef CONFIG_COMPACTION
>
> +int PageMovable(struct page *page)
> +{
> +	struct address_space *mapping;
> +
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	if (!__PageMovable(page))
> +		return 0;
> +
> +	mapping = page_mapping(page);
> +	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
> +		return 1;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(PageMovable);
> +
> +void __SetPageMovable(struct page *page, struct address_space *mapping)
> +{
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
> +	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
> +}
> +EXPORT_SYMBOL(__SetPageMovable);
> +
> +void __ClearPageMovable(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	VM_BUG_ON_PAGE(!PageMovable(page), page);
> +	page->mapping = (void *)((unsigned long)page->mapping &
> +				PAGE_MAPPING_MOVABLE);
> +}
> +EXPORT_SYMBOL(__ClearPageMovable);

The second confusing thing is that the function is named 
__ClearPageMovable(), but what it really clears is the mapping pointer,
which is not at all the opposite of what __SetPageMovable() does.

I know it's explained in the documentation, but it also deserves a 
comment here so it doesn't confuse everyone who looks at it.
Even better would be a less confusing name for the function, but I can't 
offer one right now.

> diff --git a/mm/util.c b/mm/util.c
> index 917e0e3d0f8e..b756ee36f7f0 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
>  	}
>
>  	mapping = page->mapping;

I'd probably use READ_ONCE() here to be safe. Not all callers are under 
page lock?

> -	if ((unsigned long)mapping & PAGE_MAPPING_FLAGS)
> +	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
>  		return NULL;
> -	return mapping;
> +
> +	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
>  }
> +EXPORT_SYMBOL(page_mapping);
>
>  /* Slow path of page_mapcount() for compound pages */
>  int __page_mapcount(struct page *page)
>

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#1409268 — Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration

On Mon, May 30, 2016 at 11:36:07AM +0200, Vlastimil Babka wrote:
> On 05/30/2016 03:39 AM, Minchan Kim wrote:
> >After isolation, VM calls migratepage of driver with isolated page.
> >The function of migratepage is to move content of the old page to new page
> >and set up fields of struct page newpage. Keep in mind that you should
> >clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
> >migrated the oldpage successfully and returns 0.
> 
> This "clear PG_movable" is one of the reasons I was confused about
> what __ClearPageMovable() really does. There's no actual
> "PG_movable" page flag and the function doesn't clear even the
> actual mapping flag :) Also same thing in the Documentation/ part.
> 
> Something like "... you should indicate to the VM that the oldpage
> is no longer movable via __ClearPageMovable() ..."?

It's better. I will change it.

> 
> >--- a/mm/compaction.c
> >+++ b/mm/compaction.c
> >@@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
> >
> > #ifdef CONFIG_COMPACTION
> >
> >+int PageMovable(struct page *page)
> >+{
> >+	struct address_space *mapping;
> >+
> >+	VM_BUG_ON_PAGE(!PageLocked(page), page);
> >+	if (!__PageMovable(page))
> >+		return 0;
> >+
> >+	mapping = page_mapping(page);
> >+	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
> >+		return 1;
> >+
> >+	return 0;
> >+}
> >+EXPORT_SYMBOL(PageMovable);
> >+
> >+void __SetPageMovable(struct page *page, struct address_space *mapping)
> >+{
> >+	VM_BUG_ON_PAGE(!PageLocked(page), page);
> >+	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
> >+	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
> >+}
> >+EXPORT_SYMBOL(__SetPageMovable);
> >+
> >+void __ClearPageMovable(struct page *page)
> >+{
> >+	VM_BUG_ON_PAGE(!PageLocked(page), page);
> >+	VM_BUG_ON_PAGE(!PageMovable(page), page);
> >+	page->mapping = (void *)((unsigned long)page->mapping &
> >+				PAGE_MAPPING_MOVABLE);
> >+}
> >+EXPORT_SYMBOL(__ClearPageMovable);
> 
> The second confusing thing is that the function is named
> __ClearPageMovable(), but what it really clears is the mapping
> pointer,
> which is not at all the opposite of what __SetPageMovable() does.
> 
> I know it's explained in the documentation, but it also deserves a
> comment here so it doesn't confuse everyone who looks at it.
> Even better would be a less confusing name for the function, but I
> can't offer one right now.

To me, __ClearPageMovable naming is suitable for user POV.
It effectively makes the page unmovable. The confusion is just caused
by the implementation and I don't prefer exported API depends on the
implementation. So I want to add just comment.

I didn't add comment above the function because I don't want to export
internal implementation to the user. I think they don't need to know it.

index a7df2ae71f2a..d1d2063b4fd9 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -108,6 +108,11 @@ void __ClearPageMovable(struct page *page)
 {
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        VM_BUG_ON_PAGE(!PageMovable(page), page);
+       /*
+        * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
+        * flag so that VM can catch up released page by driver after isolation.
+        * With it, VM migration doesn't try to put it back.
+        */
        page->mapping = (void *)((unsigned long)page->mapping &
                                PAGE_MAPPING_MOVABLE);

> 
> >diff --git a/mm/util.c b/mm/util.c
> >index 917e0e3d0f8e..b756ee36f7f0 100644
> >--- a/mm/util.c
> >+++ b/mm/util.c
> >@@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
> > 	}
> >
> > 	mapping = page->mapping;
> 
> I'd probably use READ_ONCE() here to be safe. Not all callers are
> under page lock?

I don't understand. Yeah, all caller are not under page lock but at least,
new user of movable pages should call it under page_lock.
Yeah, I will write the rule down in document.
In this case, what kinds of problem do you see?

> 
> >-	if ((unsigned long)mapping & PAGE_MAPPING_FLAGS)
> >+	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
> > 		return NULL;
> >-	return mapping;
> >+
> >+	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
> > }
> >+EXPORT_SYMBOL(page_mapping);
> >
> > /* Slow path of page_mapcount() for compound pages */
> > int __page_mapcount(struct page *page)
> >
> 

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#1409950 — Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration

On 05/30/2016 06:25 PM, Minchan Kim wrote:
>>> --- a/mm/compaction.c
>>> +++ b/mm/compaction.c
>>> @@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
>>>
>>> #ifdef CONFIG_COMPACTION
>>>
>>> +int PageMovable(struct page *page)
>>> +{
>>> +	struct address_space *mapping;
>>> +
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	if (!__PageMovable(page))
>>> +		return 0;
>>> +
>>> +	mapping = page_mapping(page);
>>> +	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
>>> +		return 1;
>>> +
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL(PageMovable);
>>> +
>>> +void __SetPageMovable(struct page *page, struct address_space *mapping)
>>> +{
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
>>> +	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
>>> +}
>>> +EXPORT_SYMBOL(__SetPageMovable);
>>> +
>>> +void __ClearPageMovable(struct page *page)
>>> +{
>>> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
>>> +	VM_BUG_ON_PAGE(!PageMovable(page), page);
>>> +	page->mapping = (void *)((unsigned long)page->mapping &
>>> +				PAGE_MAPPING_MOVABLE);
>>> +}
>>> +EXPORT_SYMBOL(__ClearPageMovable);
>>
>> The second confusing thing is that the function is named
>> __ClearPageMovable(), but what it really clears is the mapping
>> pointer,
>> which is not at all the opposite of what __SetPageMovable() does.
>>
>> I know it's explained in the documentation, but it also deserves a
>> comment here so it doesn't confuse everyone who looks at it.
>> Even better would be a less confusing name for the function, but I
>> can't offer one right now.
>
> To me, __ClearPageMovable naming is suitable for user POV.
> It effectively makes the page unmovable. The confusion is just caused
> by the implementation and I don't prefer exported API depends on the
> implementation. So I want to add just comment.
>
> I didn't add comment above the function because I don't want to export
> internal implementation to the user. I think they don't need to know it.
>
> index a7df2ae71f2a..d1d2063b4fd9 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -108,6 +108,11 @@ void __ClearPageMovable(struct page *page)
>  {
>         VM_BUG_ON_PAGE(!PageLocked(page), page);
>         VM_BUG_ON_PAGE(!PageMovable(page), page);
> +       /*
> +        * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
> +        * flag so that VM can catch up released page by driver after isolation.
> +        * With it, VM migration doesn't try to put it back.
> +        */
>         page->mapping = (void *)((unsigned long)page->mapping &
>                                 PAGE_MAPPING_MOVABLE);

OK, that's fine!

>>
>>> diff --git a/mm/util.c b/mm/util.c
>>> index 917e0e3d0f8e..b756ee36f7f0 100644
>>> --- a/mm/util.c
>>> +++ b/mm/util.c
>>> @@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
>>> 	}
>>>
>>> 	mapping = page->mapping;
>>
>> I'd probably use READ_ONCE() here to be safe. Not all callers are
>> under page lock?
>
> I don't understand. Yeah, all caller are not under page lock but at least,
> new user of movable pages should call it under page_lock.
> Yeah, I will write the rule down in document.
> In this case, what kinds of problem do you see?

After more thinking, probably none. It wouldn't prevent any extra races. 
Sorry for the noise.

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#1409760 — [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration

Per Vlastimi's review comment.

Thanks for the detail review, Vlastimi!
If you have another concern, feel free to say.
After I resolve all thing, I will send v7 rebased on recent mmotm.

From b14aaeeeeb2d3ac0702c7b2eec36409d74406d43 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 8 Apr 2016 10:34:49 +0900
Subject: [PATCH] mm: migrate: support non-lru movable page migration

We have allowed migration for only LRU pages until now and it was
enough to make high-order pages. But recently, embedded system(e.g.,
webOS, android) uses lots of non-movable pages(e.g., zram, GPU memory)
so we have seen several reports about troubles of small high-order
allocation. For fixing the problem, there were several efforts
(e,g,. enhance compaction algorithm, SLUB fallback to 0-order page,
reserved memory, vmalloc and so on) but if there are lots of
non-movable pages in system, their solutions are void in the long run.

So, this patch is to support facility to change non-movable pages
with movable. For the feature, this patch introduces functions related
to migration to address_space_operations as well as some page flags.

If a driver want to make own pages movable, it should define three functions
which are function pointers of struct address_space_operations.

1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);

What VM expects on isolate_page function of driver is to return *true*
if driver isolates page successfully. On returing true, VM marks the page
as PG_isolated so concurrent isolation in several CPUs skip the page
for isolation. If a driver cannot isolate the page, it should return *false*.

Once page is successfully isolated, VM uses page.lru fields so driver
shouldn't expect to preserve values in that fields.

2. int (*migratepage) (struct address_space *mapping,
		struct page *newpage, struct page *oldpage, enum migrate_mode);

After isolation, VM calls migratepage of driver with isolated page.
The function of migratepage is to move content of the old page to new page
and set up fields of struct page newpage. Keep in mind that you should
indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
under page_lock if you migrated the oldpage successfully and returns 0.
If driver cannot migrate the page at the moment, driver can return -EAGAIN.
On -EAGAIN, VM will retry page migration in a short time because VM interprets
-EAGAIN as "temporal migration failure". On returning any error except -EAGAIN,
VM will give up the page migration without retrying in this time.

Driver shouldn't touch page.lru field VM using in the functions.

3. void (*putback_page)(struct page *);

If migration fails on isolated page, VM should return the isolated page
to the driver so VM calls driver's putback_page with migration failed page.
In this function, driver should put the isolated page back to the own data
structure.

4. non-lru movable page flags

There are two page flags for supporting non-lru movable page.

* PG_movable

Driver should use the below function to make page movable under page_lock.

	void __SetPageMovable(struct page *page, struct address_space *mapping)

It needs argument of address_space for registering migration family functions
which will be called by VM. Exactly speaking, PG_movable is not a real flag of
struct page. Rather than, VM reuses page->mapping's lower bits to represent it.

	#define PAGE_MAPPING_MOVABLE 0x2
	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;

so driver shouldn't access page->mapping directly. Instead, driver should
use page_mapping which mask off the low two bits of page->mapping so it can get
right struct address_space.

For testing of non-lru movable page, VM supports __PageMovable function.
However, it doesn't guarantee to identify non-lru movable page because
page->mapping field is unified with other variables in struct page.
As well, if driver releases the page after isolation by VM, page->mapping
doesn't have stable value although it has PAGE_MAPPING_MOVABLE
(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
page is LRU or non-lru movable once the page has been isolated. Because
LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
good for just peeking to test non-lru movable pages before more expensive
checking with lock_page in pfn scanning to select victim.

For guaranteeing non-lru movable page, VM provides PageMovable function.
Unlike __PageMovable, PageMovable functions validates page->mapping and
mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
destroying of page->mapping.

Driver using __SetPageMovable should clear the flag via __ClearMovablePage
under page_lock before the releasing the page.

* PG_isolated

To prevent concurrent isolation among several CPUs, VM marks isolated page
as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
movable page, it can skip it. Driver doesn't need to manipulate the flag
because VM will set/clear it automatically. Keep in mind that if driver
sees PG_isolated page, it means the page have been isolated by VM so it
shouldn't touch page.lru field.
PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
for own purpose.

Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: John Einar Reitan <john.reitan@foss.arm.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 Documentation/filesystems/Locking |   4 +
 Documentation/filesystems/vfs.txt |  11 +++
 Documentation/vm/page_migration   | 107 ++++++++++++++++++++-
 include/linux/compaction.h        |  17 ++++
 include/linux/fs.h                |   2 +
 include/linux/ksm.h               |   3 +-
 include/linux/migrate.h           |   2 +
 include/linux/mm.h                |   1 +
 include/linux/page-flags.h        |  33 +++++--
 mm/compaction.c                   |  85 +++++++++++++----
 mm/ksm.c                          |   4 +-
 mm/migrate.c                      | 192 ++++++++++++++++++++++++++++++++++----
 mm/page_alloc.c                   |   2 +-
 mm/util.c                         |   6 +-
 14 files changed, 417 insertions(+), 52 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index af7c030a0368..3991a976cf43 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -195,7 +195,9 @@ unlocks and drops the reference.
 	int (*releasepage) (struct page *, int);
 	void (*freepage)(struct page *);
 	int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
+	bool (*isolate_page) (struct page *, isolate_mode_t);
 	int (*migratepage)(struct address_space *, struct page *, struct page *);
+	void (*putback_page) (struct page *);
 	int (*launder_page)(struct page *);
 	int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long);
 	int (*error_remove_page)(struct address_space *, struct page *);
@@ -219,7 +221,9 @@ invalidatepage:		yes
 releasepage:		yes
 freepage:		yes
 direct_IO:
+isolate_page:		yes
 migratepage:		yes (both)
+putback_page:		yes
 launder_page:		yes
 is_partially_uptodate:	yes
 error_remove_page:	yes
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 19366fef2652..9d4ae317fdcb 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -591,9 +591,14 @@ struct address_space_operations {
 	int (*releasepage) (struct page *, int);
 	void (*freepage)(struct page *);
 	ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);
+	/* isolate a page for migration */
+	bool (*isolate_page) (struct page *, isolate_mode_t);
 	/* migrate the contents of a page to the specified target */
 	int (*migratepage) (struct page *, struct page *);
+	/* put migration-failed page back to right list */
+	void (*putback_page) (struct page *);
 	int (*launder_page) (struct page *);
+
 	int (*is_partially_uptodate) (struct page *, unsigned long,
 					unsigned long);
 	void (*is_dirty_writeback) (struct page *, bool *, bool *);
@@ -739,6 +744,10 @@ struct address_space_operations {
         and transfer data directly between the storage and the
         application's address space.
 
+  isolate_page: Called by the VM when isolating a movable non-lru page.
+	If page is successfully isolated, VM marks the page as PG_isolated
+	via __SetPageIsolated.
+
   migrate_page:  This is used to compact the physical memory usage.
         If the VM wants to relocate a page (maybe off a memory card
         that is signalling imminent failure) it will pass a new page
@@ -746,6 +755,8 @@ struct address_space_operations {
 	transfer any private data across and update any references
         that it has to the page.
 
+  putback_page: Called by the VM when isolated page's migration fails.
+
   launder_page: Called before freeing a page - it writes back the dirty page. To
   	prevent redirtying the page, it is kept locked during the whole
 	operation.
diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration
index fea5c0864170..18d37c7ac50b 100644
--- a/Documentation/vm/page_migration
+++ b/Documentation/vm/page_migration
@@ -142,5 +142,110 @@ is increased so that the page cannot be freed while page migration occurs.
 20. The new page is moved to the LRU and can be scanned by the swapper
     etc again.
 
-Christoph Lameter, May 8, 2006.
+C. Non-LRU page migration
+-------------------------
+
+Although original migration aimed for reducing the latency of memory access
+for NUMA, compaction who want to create high-order page is also main customer.
+
+Current problem of the implementation is that it is designed to migrate only
+*LRU* pages. However, there are potential non-lru pages which can be migrated
+in drivers, for example, zsmalloc, virtio-balloon pages.
+
+For virtio-balloon pages, some parts of migration code path have been hooked
+up and added virtio-balloon specific functions to intercept migration logics.
+It's too specific to a driver so other drivers who want to make their pages
+movable would have to add own specific hooks in migration path.
+
+To overclome the problem, VM supports non-LRU page migration which provides
+generic functions for non-LRU movable pages without driver specific hooks
+migration path.
+
+If a driver want to make own pages movable, it should define three functions
+which are function pointers of struct address_space_operations.
+
+1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);
+
+What VM expects on isolate_page function of driver is to return *true*
+if driver isolates page successfully. On returing true, VM marks the page
+as PG_isolated so concurrent isolation in several CPUs skip the page
+for isolation. If a driver cannot isolate the page, it should return *false*.
+
+Once page is successfully isolated, VM uses page.lru fields so driver
+shouldn't expect to preserve values in that fields.
+
+2. int (*migratepage) (struct address_space *mapping,
+		struct page *newpage, struct page *oldpage, enum migrate_mode);
+
+After isolation, VM calls migratepage of driver with isolated page.
+The function of migratepage is to move content of the old page to new page
+and set up fields of struct page newpage. Keep in mind that you should
+indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
+under page_lock if you migrated the oldpage successfully and returns 0.
+If driver cannot migrate the page at the moment, driver can return -EAGAIN.
+On -EAGAIN, VM will retry page migration in a short time because VM interprets
+-EAGAIN as "temporal migration failure". On returning any error except -EAGAIN,
+VM will give up the page migration without retrying in this time.
+
+Driver shouldn't touch page.lru field VM using in the functions.
+
+3. void (*putback_page)(struct page *);
+
+If migration fails on isolated page, VM should return the isolated page
+to the driver so VM calls driver's putback_page with migration failed page.
+In this function, driver should put the isolated page back to the own data
+structure.
 
+4. non-lru movable page flags
+
+There are two page flags for supporting non-lru movable page.
+
+* PG_movable
+
+Driver should use the below function to make page movable under page_lock.
+
+	void __SetPageMovable(struct page *page, struct address_space *mapping)
+
+It needs argument of address_space for registering migration family functions
+which will be called by VM. Exactly speaking, PG_movable is not a real flag of
+struct page. Rather than, VM reuses page->mapping's lower bits to represent it.
+
+	#define PAGE_MAPPING_MOVABLE 0x2
+	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;
+
+so driver shouldn't access page->mapping directly. Instead, driver should
+use page_mapping which mask off the low two bits of page->mapping under
+page lock so it can get right struct address_space.
+
+For testing of non-lru movable page, VM supports __PageMovable function.
+However, it doesn't guarantee to identify non-lru movable page because
+page->mapping field is unified with other variables in struct page.
+As well, if driver releases the page after isolation by VM, page->mapping
+doesn't have stable value although it has PAGE_MAPPING_MOVABLE
+(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether
+page is LRU or non-lru movable once the page has been isolated. Because
+LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also
+good for just peeking to test non-lru movable pages before more expensive
+checking with lock_page in pfn scanning to select victim.
+
+For guaranteeing non-lru movable page, VM provides PageMovable function.
+Unlike __PageMovable, PageMovable functions validates page->mapping and
+mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden
+destroying of page->mapping.
+
+Driver using __SetPageMovable should clear the flag via __ClearMovablePage
+under page_lock before the releasing the page.
+
+* PG_isolated
+
+To prevent concurrent isolation among several CPUs, VM marks isolated page
+as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru
+movable page, it can skip it. Driver doesn't need to manipulate the flag
+because VM will set/clear it automatically. Keep in mind that if driver
+sees PG_isolated page, it means the page have been isolated by VM so it
+shouldn't touch page.lru field.
+PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag
+for own purpose.
+
+Christoph Lameter, May 8, 2006.
+Minchan Kim, Mar 28, 2016.
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index a58c852a268f..c6b47c861cea 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -54,6 +54,9 @@ enum compact_result {
 struct alloc_context; /* in mm/internal.h */
 
 #ifdef CONFIG_COMPACTION
+extern int PageMovable(struct page *page);
+extern void __SetPageMovable(struct page *page, struct address_space *mapping);
+extern void __ClearPageMovable(struct page *page);
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
 			void __user *buffer, size_t *length, loff_t *ppos);
@@ -151,6 +154,19 @@ extern void kcompactd_stop(int nid);
 extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx);
 
 #else
+static inline int PageMovable(struct page *page)
+{
+	return 0;
+}
+static inline void __SetPageMovable(struct page *page,
+			struct address_space *mapping)
+{
+}
+
+static inline void __ClearPageMovable(struct page *page)
+{
+}
+
 static inline enum compact_result try_to_compact_pages(gfp_t gfp_mask,
 			unsigned int order, int alloc_flags,
 			const struct alloc_context *ac,
@@ -212,6 +228,7 @@ static inline void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_i
 #endif /* CONFIG_COMPACTION */
 
 #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
+struct node;
 extern int compaction_register_node(struct node *node);
 extern void compaction_unregister_node(struct node *node);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0cfdf2aec8f7..39ef97414033 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -402,6 +402,8 @@ struct address_space_operations {
 	 */
 	int (*migratepage) (struct address_space *,
 			struct page *, struct page *, enum migrate_mode);
+	bool (*isolate_page)(struct page *, isolate_mode_t);
+	void (*putback_page)(struct page *);
 	int (*launder_page) (struct page *);
 	int (*is_partially_uptodate) (struct page *, unsigned long,
 					unsigned long);
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 7ae216a39c9e..481c8c4627ca 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -43,8 +43,7 @@ static inline struct stable_node *page_stable_node(struct page *page)
 static inline void set_page_stable_node(struct page *page,
 					struct stable_node *stable_node)
 {
-	page->mapping = (void *)stable_node +
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+	page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
 }
 
 /*
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 9b50325e4ddf..404fbfefeb33 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -37,6 +37,8 @@ extern int migrate_page(struct address_space *,
 			struct page *, struct page *, enum migrate_mode);
 extern int migrate_pages(struct list_head *l, new_page_t new, free_page_t free,
 		unsigned long private, enum migrate_mode mode, int reason);
+extern bool isolate_movable_page(struct page *page, isolate_mode_t mode);
+extern void putback_movable_page(struct page *page);
 
 extern int migrate_prep(void);
 extern int migrate_prep_local(void);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a00ec816233a..33eaec57e997 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1035,6 +1035,7 @@ static inline pgoff_t page_file_index(struct page *page)
 }
 
 bool page_mapped(struct page *page);
+struct address_space *page_mapping(struct page *page);
 
 /*
  * Return true only if the page has been allocated with
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e5a32445f930..f36dbb3a3060 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -129,6 +129,9 @@ enum pageflags {
 
 	/* Compound pages. Stored in first tail page's flags */
 	PG_double_map = PG_private_2,
+
+	/* non-lru isolated movable page */
+	PG_isolated = PG_reclaim,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -357,29 +360,37 @@ PAGEFLAG(Idle, idle, PF_ANY)
  * with the PAGE_MAPPING_ANON bit set to distinguish it.  See rmap.h.
  *
  * On an anonymous page in a VM_MERGEABLE area, if CONFIG_KSM is enabled,
- * the PAGE_MAPPING_KSM bit may be set along with the PAGE_MAPPING_ANON bit;
- * and then page->mapping points, not to an anon_vma, but to a private
+ * the PAGE_MAPPING_MOVABLE bit may be set along with the PAGE_MAPPING_ANON
+ * bit; and then page->mapping points, not to an anon_vma, but to a private
  * structure which KSM associates with that merged page.  See ksm.h.
  *
- * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is currently never used.
+ * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is used for non-lru movable
+ * page and then page->mapping points a struct address_space.
  *
  * Please note that, confusingly, "page_mapping" refers to the inode
  * address_space which maps the page from disk; whereas "page_mapped"
  * refers to user virtual address space into which the page is mapped.
  */
-#define PAGE_MAPPING_ANON	1
-#define PAGE_MAPPING_KSM	2
-#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
+#define PAGE_MAPPING_ANON	0x1
+#define PAGE_MAPPING_MOVABLE	0x2
+#define PAGE_MAPPING_KSM	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
+#define PAGE_MAPPING_FLAGS	(PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE)
 
-static __always_inline int PageAnonHead(struct page *page)
+static __always_inline int PageMappingFlags(struct page *page)
 {
-	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
+	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) != 0;
 }
 
 static __always_inline int PageAnon(struct page *page)
 {
 	page = compound_head(page);
-	return PageAnonHead(page);
+	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
+}
+
+static __always_inline int __PageMovable(struct page *page)
+{
+	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
+				PAGE_MAPPING_MOVABLE;
 }
 
 #ifdef CONFIG_KSM
@@ -393,7 +404,7 @@ static __always_inline int PageKsm(struct page *page)
 {
 	page = compound_head(page);
 	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+				PAGE_MAPPING_KSM;
 }
 #else
 TESTPAGEFLAG_FALSE(Ksm)
@@ -641,6 +652,8 @@ static inline void __ClearPageBalloon(struct page *page)
 	atomic_set(&page->_mapcount, -1);
 }
 
+__PAGEFLAG(Isolated, isolated, PF_ANY);
+
 /*
  * If network-based swap is enabled, sl*b must keep track of whether pages
  * were allocated from pfmemalloc reserves.
diff --git a/mm/compaction.c b/mm/compaction.c
index 1427366ad673..a680b52e190b 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -81,6 +81,44 @@ static inline bool migrate_async_suitable(int migratetype)
 
 #ifdef CONFIG_COMPACTION
 
+int PageMovable(struct page *page)
+{
+	struct address_space *mapping;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	if (!__PageMovable(page))
+		return 0;
+
+	mapping = page_mapping(page);
+	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
+		return 1;
+
+	return 0;
+}
+EXPORT_SYMBOL(PageMovable);
+
+void __SetPageMovable(struct page *page, struct address_space *mapping)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
+	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
+}
+EXPORT_SYMBOL(__SetPageMovable);
+
+void __ClearPageMovable(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	/*
+	 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
+	 * flag so that VM can catch up released page by driver after isolation.
+	 * With it, VM migration doesn't try to put it back.
+	 */
+	page->mapping = (void *)((unsigned long)page->mapping &
+				PAGE_MAPPING_MOVABLE);
+}
+EXPORT_SYMBOL(__ClearPageMovable);
+
 /* Do not skip compaction more than 64 times */
 #define COMPACT_MAX_DEFER_SHIFT 6
 
@@ -735,21 +773,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		}
 
 		/*
-		 * Check may be lockless but that's ok as we recheck later.
-		 * It's possible to migrate LRU pages and balloon pages
-		 * Skip any other type of page
-		 */
-		is_lru = PageLRU(page);
-		if (!is_lru) {
-			if (unlikely(balloon_page_movable(page))) {
-				if (balloon_page_isolate(page)) {
-					/* Successfully isolated */
-					goto isolate_success;
-				}
-			}
-		}
-
-		/*
 		 * Regardless of being on LRU, compound pages such as THP and
 		 * hugetlbfs are not to be compacted. We can potentially save
 		 * a lot of iterations if we skip them at once. The check is
@@ -765,8 +788,38 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			goto isolate_fail;
 		}
 
-		if (!is_lru)
+		/*
+		 * Check may be lockless but that's ok as we recheck later.
+		 * It's possible to migrate LRU and non-lru movable pages.
+		 * Skip any other type of page
+		 */
+		is_lru = PageLRU(page);
+		if (!is_lru) {
+			if (unlikely(balloon_page_movable(page))) {
+				if (balloon_page_isolate(page)) {
+					/* Successfully isolated */
+					goto isolate_success;
+				}
+			}
+
+			/*
+			 * __PageMovable can return false positive so we need
+			 * to verify it under page_lock.
+			 */
+			if (unlikely(__PageMovable(page)) &&
+					!PageIsolated(page)) {
+				if (locked) {
+					spin_unlock_irqrestore(&zone->lru_lock,
+									flags);
+					locked = false;
+				}
+
+				if (isolate_movable_page(page, isolate_mode))
+					goto isolate_success;
+			}
+
 			goto isolate_fail;
+		}
 
 		/*
 		 * Migration will fail if an anonymous page is pinned in memory,
diff --git a/mm/ksm.c b/mm/ksm.c
index 4786b4150f62..35b8aef867a9 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -532,8 +532,8 @@ static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
 	void *expected_mapping;
 	unsigned long kpfn;
 
-	expected_mapping = (void *)stable_node +
-				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
+	expected_mapping = (void *)((unsigned long)stable_node |
+					PAGE_MAPPING_KSM);
 again:
 	kpfn = READ_ONCE(stable_node->kpfn);
 	page = pfn_to_page(kpfn);
diff --git a/mm/migrate.c b/mm/migrate.c
index 2666f28b5236..60abcf379b51 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -31,6 +31,7 @@
 #include <linux/vmalloc.h>
 #include <linux/security.h>
 #include <linux/backing-dev.h>
+#include <linux/compaction.h>
 #include <linux/syscalls.h>
 #include <linux/hugetlb.h>
 #include <linux/hugetlb_cgroup.h>
@@ -73,6 +74,81 @@ int migrate_prep_local(void)
 	return 0;
 }
 
+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+	struct address_space *mapping;
+
+	/*
+	 * Avoid burning cycles with pages that are yet under __free_pages(),
+	 * or just got freed under us.
+	 *
+	 * In case we 'win' a race for a movable page being freed under us and
+	 * raise its refcount preventing __free_pages() from doing its job
+	 * the put_page() at the end of this block will take care of
+	 * release this page, thus avoiding a nasty leakage.
+	 */
+	if (unlikely(!get_page_unless_zero(page)))
+		goto out;
+
+	/*
+	 * Check PageMovable before holding a PG_lock because page's owner
+	 * assumes anybody doesn't touch PG_lock of newly allocated page
+	 * so unconditionally grapping the lock ruins page's owner side.
+	 */
+	if (unlikely(!__PageMovable(page)))
+		goto out_putpage;
+	/*
+	 * As movable pages are not isolated from LRU lists, concurrent
+	 * compaction threads can race against page migration functions
+	 * as well as race against the releasing a page.
+	 *
+	 * In order to avoid having an already isolated movable page
+	 * being (wrongly) re-isolated while it is under migration,
+	 * or to avoid attempting to isolate pages being released,
+	 * lets be sure we have the page lock
+	 * before proceeding with the movable page isolation steps.
+	 */
+	if (unlikely(!trylock_page(page)))
+		goto out_putpage;
+
+	if (!PageMovable(page) || PageIsolated(page))
+		goto out_no_isolated;
+
+	mapping = page_mapping(page);
+	VM_BUG_ON_PAGE(!mapping, page);
+
+	if (!mapping->a_ops->isolate_page(page, mode))
+		goto out_no_isolated;
+
+	/* Driver shouldn't use PG_isolated bit of page->flags */
+	WARN_ON_ONCE(PageIsolated(page));
+	__SetPageIsolated(page);
+	unlock_page(page);
+
+	return true;
+
+out_no_isolated:
+	unlock_page(page);
+out_putpage:
+	put_page(page);
+out:
+	return false;
+}
+
+/* It should be called on page which is PG_movable */
+void putback_movable_page(struct page *page)
+{
+	struct address_space *mapping;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+	mapping = page_mapping(page);
+	mapping->a_ops->putback_page(page);
+	__ClearPageIsolated(page);
+}
+
 /*
  * Put previously isolated pages back onto the appropriate lists
  * from where they were once taken off for compaction/migration.
@@ -94,10 +170,25 @@ void putback_movable_pages(struct list_head *l)
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
-		if (unlikely(isolated_balloon_page(page)))
+		if (unlikely(isolated_balloon_page(page))) {
 			balloon_page_putback(page);
-		else
+		/*
+		 * We isolated non-lru movable page so here we can use
+		 * __PageMovable because LRU page's mapping cannot have
+		 * PAGE_MAPPING_MOVABLE.
+		 */
+		} else if (unlikely(__PageMovable(page))) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		} else {
 			putback_lru_page(page);
+		}
 	}
 }
 
@@ -592,7 +683,7 @@ void migrate_page_copy(struct page *newpage, struct page *page)
  ***********************************************************/
 
 /*
- * Common logic to directly migrate a single page suitable for
+ * Common logic to directly migrate a single LRU page suitable for
  * pages that do not use PagePrivate/PagePrivate2.
  *
  * Pages are locked upon entry and exit.
@@ -755,33 +846,72 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 				enum migrate_mode mode)
 {
 	struct address_space *mapping;
-	int rc;
+	int rc = -EAGAIN;
+	bool is_lru = !__PageMovable(page);
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
 	mapping = page_mapping(page);
-	if (!mapping)
-		rc = migrate_page(mapping, newpage, page, mode);
-	else if (mapping->a_ops->migratepage)
+
+	if (likely(is_lru)) {
+		if (!mapping)
+			rc = migrate_page(mapping, newpage, page, mode);
+		else if (mapping->a_ops->migratepage)
+			/*
+			 * Most pages have a mapping and most filesystems
+			 * provide a migratepage callback. Anonymous pages
+			 * are part of swap space which also has its own
+			 * migratepage callback. This is the most common path
+			 * for page migration.
+			 */
+			rc = mapping->a_ops->migratepage(mapping, newpage,
+							page, mode);
+		else
+			rc = fallback_migrate_page(mapping, newpage,
+							page, mode);
+	} else {
 		/*
-		 * Most pages have a mapping and most filesystems provide a
-		 * migratepage callback. Anonymous pages are part of swap
-		 * space which also has its own migratepage callback. This
-		 * is the most common path for page migration.
+		 * In case of non-lru page, it could be released after
+		 * isolation step. In that case, we shouldn't try migration.
 		 */
-		rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
-	else
-		rc = fallback_migrate_page(mapping, newpage, page, mode);
+		VM_BUG_ON_PAGE(!PageIsolated(page), page);
+		if (!PageMovable(page)) {
+			rc = MIGRATEPAGE_SUCCESS;
+			__ClearPageIsolated(page);
+			goto out;
+		}
+
+		rc = mapping->a_ops->migratepage(mapping, newpage,
+						page, mode);
+		WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
+			!PageIsolated(page));
+	}
 
 	/*
 	 * When successful, old pagecache page->mapping must be cleared before
 	 * page is freed; but stats require that PageAnon be left as PageAnon.
 	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (!PageAnon(page))
+		if (__PageMovable(page)) {
+			VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+			/*
+			 * We clear PG_movable under page_lock so any compactor
+			 * cannot try to migrate this page.
+			 */
+			__ClearPageIsolated(page);
+		}
+
+		/*
+		 * Anonymous and movable page->mapping will be cleard by
+		 * free_pages_prepare so don't reset it here for keeping
+		 * the type to work PageAnon, for example.
+		 */
+		if (!PageMappingFlags(page))
 			page->mapping = NULL;
 	}
+out:
 	return rc;
 }
 
@@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	int rc = -EAGAIN;
 	int page_was_mapped = 0;
 	struct anon_vma *anon_vma = NULL;
+	bool is_lru = !__PageMovable(page);
 
 	if (!trylock_page(page)) {
 		if (!force || mode == MIGRATE_ASYNC)
@@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 		goto out_unlock_both;
 	}
 
+	if (unlikely(!is_lru)) {
+		rc = move_to_new_page(newpage, page, mode);
+		goto out_unlock_both;
+	}
+
 	/*
 	 * Corner case handling:
 	 * 1. When a new swap-cache page is read into, it is added to the LRU
@@ -920,7 +1056,8 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 	 * list in here.
 	 */
 	if (rc == MIGRATEPAGE_SUCCESS) {
-		if (unlikely(__is_movable_balloon_page(newpage)))
+		if (unlikely(__is_movable_balloon_page(newpage) ||
+				__PageMovable(newpage)))
 			put_page(newpage);
 		else
 			putback_lru_page(newpage);
@@ -961,6 +1098,12 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		/* page was freed from under us. So we are done. */
 		ClearPageActive(page);
 		ClearPageUnevictable(page);
+		if (unlikely(__PageMovable(page))) {
+			lock_page(page);
+			if (!PageMovable(page))
+				__ClearPageIsolated(page);
+			unlock_page(page);
+		}
 		if (put_new_page)
 			put_new_page(newpage, private);
 		else
@@ -1010,8 +1153,21 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 				num_poisoned_pages_inc();
 		}
 	} else {
-		if (rc != -EAGAIN)
-			putback_lru_page(page);
+		if (rc != -EAGAIN) {
+			if (likely(!__PageMovable(page))) {
+				putback_lru_page(page);
+				goto put_new;
+			}
+
+			lock_page(page);
+			if (PageMovable(page))
+				putback_movable_page(page);
+			else
+				__ClearPageIsolated(page);
+			unlock_page(page);
+			put_page(page);
+		}
+put_new:
 		if (put_new_page)
 			put_new_page(newpage, private);
 		else
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d27e8b968ac3..4d0ba8f6cfee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1014,7 +1014,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
 			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
-	if (PageAnonHead(page))
+	if (PageMappingFlags(page))
 		page->mapping = NULL;
 	if (check_free)
 		bad += free_pages_check(page);
diff --git a/mm/util.c b/mm/util.c
index 917e0e3d0f8e..b756ee36f7f0 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
 	}
 
 	mapping = page->mapping;
-	if ((unsigned long)mapping & PAGE_MAPPING_FLAGS)
+	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
 		return NULL;
-	return mapping;
+
+	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
 }
+EXPORT_SYMBOL(page_mapping);
 
 /* Slow path of page_mapcount() for compound pages */
 int __page_mapcount(struct page *page)
-- 
1.9.1

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#1409951 — Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration

On 05/31/2016 02:01 AM, Minchan Kim wrote:
> Per Vlastimi's review comment.
>
> Thanks for the detail review, Vlastimi!
> If you have another concern, feel free to say.

I don't for now :)

[...]

> Cc: Rik van Riel <riel@redhat.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Rafael Aquini <aquini@redhat.com>
> Cc: virtualization@lists.linux-foundation.org
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: John Einar Reitan <john.reitan@foss.arm.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

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#1410673 — Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration

On Tue, May 31, 2016 at 09:52:48AM +0200, Vlastimil Babka wrote:
> On 05/31/2016 02:01 AM, Minchan Kim wrote:
> >Per Vlastimi's review comment.
> >
> >Thanks for the detail review, Vlastimi!
> >If you have another concern, feel free to say.
> 
> I don't for now :)
> 
> [...]
> 
> >Cc: Rik van Riel <riel@redhat.com>
> >Cc: Vlastimil Babka <vbabka@suse.cz>
> >Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >Cc: Mel Gorman <mgorman@suse.de>
> >Cc: Hugh Dickins <hughd@google.com>
> >Cc: Rafael Aquini <aquini@redhat.com>
> >Cc: virtualization@lists.linux-foundation.org
> >Cc: Jonathan Corbet <corbet@lwn.net>
> >Cc: John Einar Reitan <john.reitan@foss.arm.com>
> >Cc: dri-devel@lists.freedesktop.org
> >Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> >Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks for the review, Vlastimil!

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#1404502 — [PATCH v6 10/12] zsmalloc: use freeobj for index

Zsmalloc stores first free object's <PFN, obj_idx> position into
freeobj in each zspage. If we change it with index from first_page
instead of position, it makes page migration simple because we
don't need to correct other entries for linked list if a page is
migrated out.

Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 139 ++++++++++++++++++++++++++++++----------------------------
 1 file changed, 73 insertions(+), 66 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 8fc16cc4d76d..a5da5edfc1d0 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -69,9 +69,7 @@
  * Object location (<PFN>, <obj_idx>) is encoded as
  * as single (unsigned long) handle value.
  *
- * Note that object index <obj_idx> is relative to system
- * page <PFN> it is stored in, so for each sub-page belonging
- * to a zspage, obj_idx starts with 0.
+ * Note that object index <obj_idx> starts from 0.
  *
  * This is made more complicated by various memory models and PAE.
  */
@@ -212,10 +210,10 @@ struct size_class {
 struct link_free {
 	union {
 		/*
-		 * Position of next free chunk (encodes <PFN, obj_idx>)
+		 * Free object index;
 		 * It's valid for non-allocated object
 		 */
-		void *next;
+		unsigned long next;
 		/*
 		 * Handle of allocated object.
 		 */
@@ -259,7 +257,7 @@ struct zspage {
 		unsigned int class:CLASS_BITS;
 	};
 	unsigned int inuse;
-	void *freeobj;
+	unsigned int freeobj;
 	struct page *first_page;
 	struct list_head list; /* fullness list */
 };
@@ -457,14 +455,14 @@ static inline void set_first_obj_offset(struct page *page, int offset)
 	page->index = offset;
 }
 
-static inline unsigned long get_freeobj(struct zspage *zspage)
+static inline unsigned int get_freeobj(struct zspage *zspage)
 {
-	return (unsigned long)zspage->freeobj;
+	return zspage->freeobj;
 }
 
-static inline void set_freeobj(struct zspage *zspage, unsigned long obj)
+static inline void set_freeobj(struct zspage *zspage, unsigned int obj)
 {
-	zspage->freeobj = (void *)obj;
+	zspage->freeobj = obj;
 }
 
 static void get_zspage_mapping(struct zspage *zspage,
@@ -806,6 +804,10 @@ static int get_pages_per_zspage(int class_size)
 	return max_usedpc_order;
 }
 
+static struct page *get_first_page(struct zspage *zspage)
+{
+	return zspage->first_page;
+}
 
 static struct zspage *get_zspage(struct page *page)
 {
@@ -817,37 +819,33 @@ static struct page *get_next_page(struct page *page)
 	return page->next;
 }
 
-/*
- * Encode <page, obj_idx> as a single handle value.
- * We use the least bit of handle for tagging.
+/**
+ * obj_to_location - get (<page>, <obj_idx>) from encoded object value
+ * @page: page object resides in zspage
+ * @obj_idx: object index
  */
-static void *location_to_obj(struct page *page, unsigned long obj_idx)
+static void obj_to_location(unsigned long obj, struct page **page,
+				unsigned int *obj_idx)
 {
-	unsigned long obj;
+	obj >>= OBJ_TAG_BITS;
+	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
+	*obj_idx = (obj & OBJ_INDEX_MASK);
+}
 
-	if (!page) {
-		VM_BUG_ON(obj_idx);
-		return NULL;
-	}
+/**
+ * location_to_obj - get obj value encoded from (<page>, <obj_idx>)
+ * @page: page object resides in zspage
+ * @obj_idx: object index
+ */
+static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
+{
+	unsigned long obj;
 
 	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
-	obj |= ((obj_idx) & OBJ_INDEX_MASK);
+	obj |= obj_idx & OBJ_INDEX_MASK;
 	obj <<= OBJ_TAG_BITS;
 
-	return (void *)obj;
-}
-
-/*
- * Decode <page, obj_idx> pair from the given object handle. We adjust the
- * decoded obj_idx back to its original value since it was adjusted in
- * location_to_obj().
- */
-static void obj_to_location(unsigned long obj, struct page **page,
-				unsigned long *obj_idx)
-{
-	obj >>= OBJ_TAG_BITS;
-	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
-	*obj_idx = (obj & OBJ_INDEX_MASK);
+	return obj;
 }
 
 static unsigned long handle_to_obj(unsigned long handle)
@@ -865,16 +863,6 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
 		return *(unsigned long *)obj;
 }
 
-static unsigned long obj_idx_to_offset(struct page *page,
-				unsigned long obj_idx, int class_size)
-{
-	unsigned long off;
-
-	off = get_first_obj_offset(page);
-
-	return off + obj_idx * class_size;
-}
-
 static inline int trypin_tag(unsigned long handle)
 {
 	return bit_spin_trylock(HANDLE_PIN_BIT, (unsigned long *)handle);
@@ -918,13 +906,13 @@ static void free_zspage(struct zs_pool *pool, struct zspage *zspage)
 /* Initialize a newly allocated zspage */
 static void init_zspage(struct size_class *class, struct zspage *zspage)
 {
+	unsigned int freeobj = 1;
 	unsigned long off = 0;
 	struct page *page = zspage->first_page;
 
 	while (page) {
 		struct page *next_page;
 		struct link_free *link;
-		unsigned int i = 1;
 		void *vaddr;
 
 		set_first_obj_offset(page, off);
@@ -933,7 +921,7 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		link = (struct link_free *)vaddr + off / sizeof(*link);
 
 		while ((off += class->size) < PAGE_SIZE) {
-			link->next = location_to_obj(page, i++);
+			link->next = freeobj++ << OBJ_ALLOCATED_TAG;
 			link += class->size / sizeof(*link);
 		}
 
@@ -943,14 +931,21 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		 * page (if present)
 		 */
 		next_page = get_next_page(page);
-		link->next = location_to_obj(next_page, 0);
+		if (next_page) {
+			link->next = freeobj++ << OBJ_ALLOCATED_TAG;
+		} else {
+			/*
+			 * Reset OBJ_ALLOCATED_TAG bit to last link to tell
+			 * whether it's allocated object or not.
+			 */
+			link->next = -1 << OBJ_ALLOCATED_TAG;
+		}
 		kunmap_atomic(vaddr);
 		page = next_page;
 		off %= PAGE_SIZE;
 	}
 
-	set_freeobj(zspage,
-		(unsigned long)location_to_obj(zspage->first_page, 0));
+	set_freeobj(zspage, 0);
 }
 
 static void create_page_chain(struct zspage *zspage, struct page *pages[],
@@ -1267,7 +1262,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 {
 	struct zspage *zspage;
 	struct page *page;
-	unsigned long obj, obj_idx, off;
+	unsigned long obj, off;
+	unsigned int obj_idx;
 
 	unsigned int class_idx;
 	enum fullness_group fg;
@@ -1291,7 +1287,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	zspage = get_zspage(page);
 	get_zspage_mapping(zspage, &class_idx, &fg);
 	class = pool->size_class[class_idx];
-	off = obj_idx_to_offset(page, obj_idx, class->size);
+	off = (class->size * obj_idx) & ~PAGE_MASK;
 
 	area = &get_cpu_var(zs_map_area);
 	area->vm_mm = mm;
@@ -1320,7 +1316,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 {
 	struct zspage *zspage;
 	struct page *page;
-	unsigned long obj, obj_idx, off;
+	unsigned long obj, off;
+	unsigned int obj_idx;
 
 	unsigned int class_idx;
 	enum fullness_group fg;
@@ -1332,7 +1329,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
 	zspage = get_zspage(page);
 	get_zspage_mapping(zspage, &class_idx, &fg);
 	class = pool->size_class[class_idx];
-	off = obj_idx_to_offset(page, obj_idx, class->size);
+	off = (class->size * obj_idx) & ~PAGE_MASK;
 
 	area = this_cpu_ptr(&zs_map_area);
 	if (off + class->size <= PAGE_SIZE)
@@ -1354,21 +1351,28 @@ EXPORT_SYMBOL_GPL(zs_unmap_object);
 static unsigned long obj_malloc(struct size_class *class,
 				struct zspage *zspage, unsigned long handle)
 {
+	int i, nr_page, offset;
 	unsigned long obj;
 	struct link_free *link;
 
 	struct page *m_page;
-	unsigned long m_objidx, m_offset;
+	unsigned long m_offset;
 	void *vaddr;
 
 	handle |= OBJ_ALLOCATED_TAG;
 	obj = get_freeobj(zspage);
-	obj_to_location(obj, &m_page, &m_objidx);
-	m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
+
+	offset = obj * class->size;
+	nr_page = offset >> PAGE_SHIFT;
+	m_offset = offset & ~PAGE_MASK;
+	m_page = get_first_page(zspage);
+
+	for (i = 0; i < nr_page; i++)
+		m_page = get_next_page(m_page);
 
 	vaddr = kmap_atomic(m_page);
 	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
-	set_freeobj(zspage, (unsigned long)link->next);
+	set_freeobj(zspage, link->next >> OBJ_ALLOCATED_TAG);
 	if (!class->huge)
 		/* record handle in the header of allocated chunk */
 		link->handle = handle;
@@ -1380,6 +1384,8 @@ static unsigned long obj_malloc(struct size_class *class,
 	mod_zspage_inuse(zspage, 1);
 	zs_stat_inc(class, OBJ_USED, 1);
 
+	obj = location_to_obj(m_page, obj);
+
 	return obj;
 }
 
@@ -1445,22 +1451,22 @@ static void obj_free(struct size_class *class, unsigned long obj)
 	struct link_free *link;
 	struct zspage *zspage;
 	struct page *f_page;
-	unsigned long f_objidx, f_offset;
+	unsigned long f_offset;
+	unsigned int f_objidx;
 	void *vaddr;
 
 	obj &= ~OBJ_ALLOCATED_TAG;
 	obj_to_location(obj, &f_page, &f_objidx);
+	f_offset = (class->size * f_objidx) & ~PAGE_MASK;
 	zspage = get_zspage(f_page);
 
-	f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);
-
 	vaddr = kmap_atomic(f_page);
 
 	/* Insert this object in containing zspage's freelist */
 	link = (struct link_free *)(vaddr + f_offset);
-	link->next = (void *)get_freeobj(zspage);
+	link->next = get_freeobj(zspage) << OBJ_ALLOCATED_TAG;
 	kunmap_atomic(vaddr);
-	set_freeobj(zspage, obj);
+	set_freeobj(zspage, f_objidx);
 	mod_zspage_inuse(zspage, -1);
 	zs_stat_dec(class, OBJ_USED, 1);
 }
@@ -1469,7 +1475,8 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
 {
 	struct zspage *zspage;
 	struct page *f_page;
-	unsigned long obj, f_objidx;
+	unsigned long obj;
+	unsigned int f_objidx;
 	int class_idx;
 	struct size_class *class;
 	enum fullness_group fullness;
@@ -1506,7 +1513,7 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 				unsigned long src)
 {
 	struct page *s_page, *d_page;
-	unsigned long s_objidx, d_objidx;
+	unsigned int s_objidx, d_objidx;
 	unsigned long s_off, d_off;
 	void *s_addr, *d_addr;
 	int s_size, d_size, size;
@@ -1517,8 +1524,8 @@ static void zs_object_copy(struct size_class *class, unsigned long dst,
 	obj_to_location(src, &s_page, &s_objidx);
 	obj_to_location(dst, &d_page, &d_objidx);
 
-	s_off = obj_idx_to_offset(s_page, s_objidx, class->size);
-	d_off = obj_idx_to_offset(d_page, d_objidx, class->size);
+	s_off = (class->size * s_objidx) & ~PAGE_MASK;
+	d_off = (class->size * d_objidx) & ~PAGE_MASK;
 
 	if (s_off + class->size > PAGE_SIZE)
 		s_size = PAGE_SIZE - s_off;
-- 
1.9.1

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#1404504 — [PATCH v6 09/12] zsmalloc: separate free_zspage from putback_zspage

Currently, putback_zspage does free zspage under class->lock
if fullness become ZS_EMPTY but it makes trouble to implement
locking scheme for new zspage migration.
So, this patch is to separate free_zspage from putback_zspage
and free zspage out of class->lock which is preparation for
zspage migration.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index b24842bd4537..8fc16cc4d76d 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1683,14 +1683,12 @@ static struct zspage *isolate_zspage(struct size_class *class, bool source)
 
 /*
  * putback_zspage - add @zspage into right class's fullness list
- * @pool: target pool
  * @class: destination class
  * @zspage: target page
  *
  * Return @zspage's fullness_group
  */
-static enum fullness_group putback_zspage(struct zs_pool *pool,
-			struct size_class *class,
+static enum fullness_group putback_zspage(struct size_class *class,
 			struct zspage *zspage)
 {
 	enum fullness_group fullness;
@@ -1699,15 +1697,6 @@ static enum fullness_group putback_zspage(struct zs_pool *pool,
 	insert_zspage(class, zspage, fullness);
 	set_zspage_mapping(zspage, class->index, fullness);
 
-	if (fullness == ZS_EMPTY) {
-		zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
-			class->size, class->pages_per_zspage));
-		atomic_long_sub(class->pages_per_zspage,
-				&pool->pages_allocated);
-
-		free_zspage(pool, zspage);
-	}
-
 	return fullness;
 }
 
@@ -1756,23 +1745,29 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
 			if (!migrate_zspage(pool, class, &cc))
 				break;
 
-			putback_zspage(pool, class, dst_zspage);
+			putback_zspage(class, dst_zspage);
 		}
 
 		/* Stop if we couldn't find slot */
 		if (dst_zspage == NULL)
 			break;
 
-		putback_zspage(pool, class, dst_zspage);
-		if (putback_zspage(pool, class, src_zspage) == ZS_EMPTY)
+		putback_zspage(class, dst_zspage);
+		if (putback_zspage(class, src_zspage) == ZS_EMPTY) {
+			zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
+					class->size, class->pages_per_zspage));
+			atomic_long_sub(class->pages_per_zspage,
+					&pool->pages_allocated);
+			free_zspage(pool, src_zspage);
 			pool->stats.pages_compacted += class->pages_per_zspage;
+		}
 		spin_unlock(&class->lock);
 		cond_resched();
 		spin_lock(&class->lock);
 	}
 
 	if (src_zspage)
-		putback_zspage(pool, class, src_zspage);
+		putback_zspage(class, src_zspage);
 
 	spin_unlock(&class->lock);
 }
-- 
1.9.1

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#1404505 — [PATCH v6 04/12] zsmalloc: keep max_object in size_class

Every zspage in a size_class has same number of max objects so
we could move it to a size_class.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 72698db958e7..73a1eb4ffddf 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -32,8 +32,6 @@
  *	page->freelist: points to the first free object in zspage.
  *		Free objects are linked together using in-place
  *		metadata.
- *	page->objects: maximum number of objects we can store in this
- *		zspage (class->zspage_order * PAGE_SIZE / class->size)
  *	page->lru: links together first pages of various zspages.
  *		Basically forming list of zspages in a fullness group.
  *	page->mapping: class index and fullness group of the zspage
@@ -211,6 +209,7 @@ struct size_class {
 	 * of ZS_ALIGN.
 	 */
 	int size;
+	int objs_per_zspage;
 	unsigned int index;
 
 	struct zs_size_stat stats;
@@ -627,21 +626,22 @@ static inline void zs_pool_stat_destroy(struct zs_pool *pool)
  * the pool (not yet implemented). This function returns fullness
  * status of the given page.
  */
-static enum fullness_group get_fullness_group(struct page *first_page)
+static enum fullness_group get_fullness_group(struct size_class *class,
+						struct page *first_page)
 {
-	int inuse, max_objects;
+	int inuse, objs_per_zspage;
 	enum fullness_group fg;
 
 	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
 
 	inuse = first_page->inuse;
-	max_objects = first_page->objects;
+	objs_per_zspage = class->objs_per_zspage;
 
 	if (inuse == 0)
 		fg = ZS_EMPTY;
-	else if (inuse == max_objects)
+	else if (inuse == objs_per_zspage)
 		fg = ZS_FULL;
-	else if (inuse <= 3 * max_objects / fullness_threshold_frac)
+	else if (inuse <= 3 * objs_per_zspage / fullness_threshold_frac)
 		fg = ZS_ALMOST_EMPTY;
 	else
 		fg = ZS_ALMOST_FULL;
@@ -728,7 +728,7 @@ static enum fullness_group fix_fullness_group(struct size_class *class,
 	enum fullness_group currfg, newfg;
 
 	get_zspage_mapping(first_page, &class_idx, &currfg);
-	newfg = get_fullness_group(first_page);
+	newfg = get_fullness_group(class, first_page);
 	if (newfg == currfg)
 		goto out;
 
@@ -1008,9 +1008,6 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
 	init_zspage(class, first_page);
 
 	first_page->freelist = location_to_obj(first_page, 0);
-	/* Maximum number of objects we can store in this zspage */
-	first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;
-
 	error = 0; /* Success */
 
 cleanup:
@@ -1238,11 +1235,11 @@ static bool can_merge(struct size_class *prev, int size, int pages_per_zspage)
 	return true;
 }
 
-static bool zspage_full(struct page *first_page)
+static bool zspage_full(struct size_class *class, struct page *first_page)
 {
 	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
 
-	return first_page->inuse == first_page->objects;
+	return first_page->inuse == class->objs_per_zspage;
 }
 
 unsigned long zs_get_total_pages(struct zs_pool *pool)
@@ -1628,7 +1625,7 @@ static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
 		}
 
 		/* Stop if there is no more space */
-		if (zspage_full(d_page)) {
+		if (zspage_full(class, d_page)) {
 			unpin_tag(handle);
 			ret = -ENOMEM;
 			break;
@@ -1687,7 +1684,7 @@ static enum fullness_group putback_zspage(struct zs_pool *pool,
 {
 	enum fullness_group fullness;
 
-	fullness = get_fullness_group(first_page);
+	fullness = get_fullness_group(class, first_page);
 	insert_zspage(class, fullness, first_page);
 	set_zspage_mapping(first_page, class->index, fullness);
 
@@ -1939,8 +1936,9 @@ struct zs_pool *zs_create_pool(const char *name)
 		class->size = size;
 		class->index = i;
 		class->pages_per_zspage = pages_per_zspage;
-		if (pages_per_zspage == 1 &&
-			get_maxobj_per_zspage(size, pages_per_zspage) == 1)
+		class->objs_per_zspage = class->pages_per_zspage *
+						PAGE_SIZE / class->size;
+		if (pages_per_zspage == 1 && class->objs_per_zspage == 1)
 			class->huge = true;
 		spin_lock_init(&class->lock);
 		pool->size_class[i] = class;
-- 
1.9.1

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#1404506 — [PATCH v6 01/12] mm: use put_page to free page instead of putback_lru_page

Procedure of page migration is as follows:

First of all, it should isolate a page from LRU and try to
migrate the page. If it is successful, it releases the page
for freeing. Otherwise, it should put the page back to LRU
list.

For LRU pages, we have used putback_lru_page for both freeing
and putback to LRU list. It's okay because put_page is aware of
LRU list so if it releases last refcount of the page, it removes
the page from LRU list. However, It makes unnecessary operations
(e.g., lru_cache_add, pagevec and flags operations. It would be
not significant but no worth to do) and harder to support new
non-lru page migration because put_page isn't aware of non-lru
page's data structure.

To solve the problem, we can add new hook in put_page with
PageMovable flags check but it can increase overhead in
hot path and needs new locking scheme to stabilize the flag check
with put_page.

So, this patch cleans it up to divide two semantic(ie, put and putback).
If migration is successful, use put_page instead of putback_lru_page and
use putback_lru_page only on failure. That makes code more readable
and doesn't add overhead in put_page.

Comment from Vlastimil
"Yeah, and compaction (perhaps also other migration users) has to drain
the lru pvec... Getting rid of this stuff is worth even by itself."

Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/migrate.c | 64 +++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 9baf41c877ff..2666f28b5236 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -913,6 +913,19 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 		put_anon_vma(anon_vma);
 	unlock_page(page);
 out:
+	/*
+	 * If migration is successful, decrease refcount of the newpage
+	 * which will not free the page because new page owner increased
+	 * refcounter. As well, if it is LRU page, add the page to LRU
+	 * list in here.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		if (unlikely(__is_movable_balloon_page(newpage)))
+			put_page(newpage);
+		else
+			putback_lru_page(newpage);
+	}
+
 	return rc;
 }
 
@@ -946,6 +959,12 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 
 	if (page_count(page) == 1) {
 		/* page was freed from under us. So we are done. */
+		ClearPageActive(page);
+		ClearPageUnevictable(page);
+		if (put_new_page)
+			put_new_page(newpage, private);
+		else
+			put_page(newpage);
 		goto out;
 	}
 
@@ -958,10 +977,8 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 	}
 
 	rc = __unmap_and_move(page, newpage, force, mode);
-	if (rc == MIGRATEPAGE_SUCCESS) {
-		put_new_page = NULL;
+	if (rc == MIGRATEPAGE_SUCCESS)
 		set_page_owner_migrate_reason(newpage, reason);
-	}
 
 out:
 	if (rc != -EAGAIN) {
@@ -974,34 +991,33 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
 		list_del(&page->lru);
 		dec_zone_page_state(page, NR_ISOLATED_ANON +
 				page_is_file_cache(page));
-		/* Soft-offlined page shouldn't go through lru cache list */
-		if (reason == MR_MEMORY_FAILURE && rc == MIGRATEPAGE_SUCCESS) {
+	}
+
+	/*
+	 * If migration is successful, releases reference grabbed during
+	 * isolation. Otherwise, restore the page to right list unless
+	 * we want to retry.
+	 */
+	if (rc == MIGRATEPAGE_SUCCESS) {
+		put_page(page);
+		if (reason == MR_MEMORY_FAILURE) {
 			/*
-			 * With this release, we free successfully migrated
-			 * page and set PG_HWPoison on just freed page
-			 * intentionally. Although it's rather weird, it's how
-			 * HWPoison flag works at the moment.
+			 * Set PG_HWPoison on just freed page
+			 * intentionally. Although it's rather weird,
+			 * it's how HWPoison flag works at the moment.
 			 */
-			put_page(page);
 			if (!test_set_page_hwpoison(page))
 				num_poisoned_pages_inc();
-		} else
+		}
+	} else {
+		if (rc != -EAGAIN)
 			putback_lru_page(page);
+		if (put_new_page)
+			put_new_page(newpage, private);
+		else
+			put_page(newpage);
 	}
 
-	/*
-	 * If migration was not successful and there's a freeing callback, use
-	 * it.  Otherwise, putback_lru_page() will drop the reference grabbed
-	 * during isolation.
-	 */
-	if (put_new_page)
-		put_new_page(newpage, private);
-	else if (unlikely(__is_movable_balloon_page(newpage))) {
-		/* drop our reference, page already in the balloon */
-		put_page(newpage);
-	} else
-		putback_lru_page(newpage);
-
 	if (result) {
 		if (rc)
 			*result = rc;
-- 
1.9.1

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#1404508 — [PATCH v6 07/12] zsmalloc: factor page chain functionality out

For page migration, we need to create page chain of zspage dynamically
so this patch factors it out from alloc_zspage.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 mm/zsmalloc.c | 59 +++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 35 insertions(+), 24 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index cb342882cde3..2d1e4961905e 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -956,7 +956,8 @@ static void init_zspage(struct size_class *class, struct page *first_page)
 	unsigned long off = 0;
 	struct page *page = first_page;
 
-	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
+	first_page->freelist = NULL;
+	set_zspage_inuse(first_page, 0);
 
 	while (page) {
 		struct page *next_page;
@@ -992,15 +993,16 @@ static void init_zspage(struct size_class *class, struct page *first_page)
 		page = next_page;
 		off %= PAGE_SIZE;
 	}
+
+	set_freeobj(first_page, (unsigned long)location_to_obj(first_page, 0));
 }
 
-/*
- * Allocate a zspage for the given size class
- */
-static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
+static void create_page_chain(struct page *pages[], int nr_pages)
 {
-	int i, error;
-	struct page *first_page = NULL, *uninitialized_var(prev_page);
+	int i;
+	struct page *page;
+	struct page *prev_page = NULL;
+	struct page *first_page = NULL;
 
 	/*
 	 * Allocate individual pages and link them together as:
@@ -1013,20 +1015,14 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
 	 * (i.e. no other sub-page has this flag set) and PG_private_2 to
 	 * identify the last page.
 	 */
-	error = -ENOMEM;
-	for (i = 0; i < class->pages_per_zspage; i++) {
-		struct page *page;
-
-		page = alloc_page(flags);
-		if (!page)
-			goto cleanup;
+	for (i = 0; i < nr_pages; i++) {
+		page = pages[i];
 
 		INIT_LIST_HEAD(&page->lru);
-		if (i == 0) {	/* first page */
+		if (i == 0) {
 			SetPagePrivate(page);
 			set_page_private(page, 0);
 			first_page = page;
-			set_zspage_inuse(first_page, 0);
 		}
 		if (i == 1)
 			set_page_private(first_page, (unsigned long)page);
@@ -1034,22 +1030,37 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
 			set_page_private(page, (unsigned long)first_page);
 		if (i >= 2)
 			list_add(&page->lru, &prev_page->lru);
-		if (i == class->pages_per_zspage - 1)	/* last page */
+		if (i == nr_pages - 1)
 			SetPagePrivate2(page);
 		prev_page = page;
 	}
+}
 
-	init_zspage(class, first_page);
+/*
+ * Allocate a zspage for the given size class
+ */
+static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
+{
+	int i;
+	struct page *first_page = NULL;
+	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE];
 
-	set_freeobj(first_page,	(unsigned long)location_to_obj(first_page, 0));
-	error = 0; /* Success */
+	for (i = 0; i < class->pages_per_zspage; i++) {
+		struct page *page;
 
-cleanup:
-	if (unlikely(error) && first_page) {
-		free_zspage(first_page);
-		first_page = NULL;
+		page = alloc_page(flags);
+		if (!page) {
+			while (--i >= 0)
+				__free_page(pages[i]);
+			return NULL;
+		}
+		pages[i] = page;
 	}
 
+	create_page_chain(pages, class->pages_per_zspage);
+	first_page = pages[0];
+	init_zspage(class, first_page);
+
 	return first_page;
 }
 
-- 
1.9.1

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