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[RFC 00/11] THP swap: Delay splitting THP during swapping out

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  [RFC 00/11] THP swap: Delay splitting THP during swapping out "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:40 +0200
    [RFC 09/11] mm, THP: Add can_split_huge_page() "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:40 +0200
    [RFC 08/11] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:40 +0200
    [RFC 11/11] mm, THP, swap: Delay splitting THP during swap out "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:40 +0200
    [RFC 04/11] mm, memcg: Support to charge/uncharge multiple swap entries "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    [RFC 02/11] swap: Change SWAPFILE_CLUSTER to 512 "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    [RFC 03/11] mm, memcg: Add swap_cgroup_iter iterator "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    [RFC 01/11] swap: Add swap_cluster_list "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    [RFC 06/11] mm, THP, swap: Add get_huge_swap_page() "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    [RFC 05/11] mm, THP, swap: Add swap cluster allocate/free functions "Huang, Ying" <ying.huang@intel.com> - 2016-08-09 18:50 +0200
    Re: [RFC 00/11] THP swap: Delay splitting THP during swapping out "Huang\, Ying" <ying.huang@intel.com> - 2016-08-09 19:30 +0200

#1458938 — [RFC 00/11] THP swap: Delay splitting THP during swapping out

From: Huang Ying <ying.huang@intel.com>

This patchset is based on 8/4 head of mmotm/master.

This is the first step for Transparent Huge Page (THP) swap support.
The plan is to delaying splitting THP step by step and avoid splitting
THP finally during THP swapping out and swapping in.

The advantages of THP swap support are:

- Batch swap operations for THP to reduce lock acquiring/releasing,
  including allocating/freeing swap space, adding/deleting to/from swap
  cache, and writing/reading swap space, etc.

- THP swap space read/write will be 2M sequence IO.  It is particularly
  helpful for swap read, which usually are 4k random IO.

- It will help memory fragmentation, especially when THP is heavily used
  by the applications.  2M continuous pages will be free up after THP
  swapping out.

As the first step, in this patchset, the splitting huge page is
delayed from almost the first step of swapping out to after allocating
the swap space for THP and adding the THP into swap cache.  This will
reduce lock acquiring/releasing for locks used for swap space and swap
cache management.

With the patchset, the swap out bandwidth improved 12.1% in
vm-scalability swap-w-seq test case with 16 processes on a Xeon E5 v3
system.  To test sequence swap out, the test case uses 16 processes
sequentially allocate and write to anonymous pages until RAM and part of
the swap device is used up.

The detailed compare result is as follow,

base             base+patchset
---------------- -------------------------- 
         %stddev     %change         %stddev
             \          |                \  
   1118821 ±  0%     +12.1%    1254241 ±  1%  vmstat.swap.so
   2460636 ±  1%     +10.6%    2720983 ±  1%  vm-scalability.throughput
    308.79 ±  1%      -7.9%     284.53 ±  1%  vm-scalability.time.elapsed_time
      1639 ±  4%    +232.3%       5446 ±  1%  meminfo.SwapCached
      0.70 ±  3%      +8.7%       0.77 ±  5%  perf-stat.ipc
      9.82 ±  8%     -31.6%       6.72 ±  2%  perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list

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#1458939 — [RFC 09/11] mm, THP: Add can_split_huge_page()

From: Huang Ying <ying.huang@intel.com>

Separates checking whether we can split the huge page from
split_huge_page_to_list() into a function.  This will help to check that
before splitting the THP (Transparent Huge Page) really.

This will be used for delaying splitting THP during swapping out.  Where
for a THP, we will allocate a swap cluster, add the THP into swap cache,
then split the THP.  To avoid unnecessary operations for un-splittable
THP, we will check that firstly.

There is no functionality change in this patch.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/huge_mm.h |  6 ++++++
 mm/huge_memory.c        | 13 ++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 6f14de4..95ccbb4 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -90,6 +90,7 @@ extern unsigned long transparent_hugepage_flags;
 extern void prep_transhuge_page(struct page *page);
 extern void free_transhuge_page(struct page *page);
 
+bool can_split_huge_page(struct page *page);
 int split_huge_page_to_list(struct page *page, struct list_head *list);
 static inline int split_huge_page(struct page *page)
 {
@@ -169,6 +170,11 @@ void put_huge_zero_page(void);
 static inline void prep_transhuge_page(struct page *page) {}
 
 #define transparent_hugepage_flags 0UL
+static inline bool
+can_split_huge_page(struct page *page)
+{
+	return false;
+}
 static inline int
 split_huge_page_to_list(struct page *page, struct list_head *list)
 {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2373f0a..af65413 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1954,6 +1954,17 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
 	return ret;
 }
 
+/* Racy check whether the huge page can be split */
+bool can_split_huge_page(struct page *page)
+{
+	int extra_pins = 0;
+
+	/* Additional pins from radix tree */
+	if (!PageAnon(page))
+		extra_pins = HPAGE_PMD_NR;
+	return total_mapcount(page) == page_count(page) - extra_pins - 1;
+}
+
 /*
  * This function splits huge page into normal pages. @page can point to any
  * subpage of huge page to split. Split doesn't change the position of @page.
@@ -2024,7 +2035,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	 * Racy check if we can split the page, before freeze_page() will
 	 * split PMDs
 	 */
-	if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
+	if (!can_split_huge_page(head)) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}
-- 
2.8.1

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#1458945 — [RFC 08/11] mm, THP, swap: Support to add/delete THP to/from swap cache

From: Huang Ying <ying.huang@intel.com>

With this patch, a THP (Transparent Huge Page) can be added/deleted
to/from swap cache as a set of sub-pages (512 on x86_64).

This will be used for Transparent Huge Page (THP) swap support.  Where
one THP may be added/delted to/from the swap cache.  This will batch
swap cache operations to reduce the lock acquire/release times for THP
swap too.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/page-flags.h |  2 +-
 mm/swap_state.c            | 57 +++++++++++++++++++++++++++++++---------------
 2 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 74e4dda..f5bcbea 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -314,7 +314,7 @@ PAGEFLAG_FALSE(HighMem)
 #endif
 
 #ifdef CONFIG_SWAP
-PAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
+PAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)
 #else
 PAGEFLAG_FALSE(SwapCache)
 #endif
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 2013793..a41fd10 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -41,6 +41,7 @@ struct address_space swapper_spaces[MAX_SWAPFILES] = {
 };
 
 #define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)
+#define ADD_CACHE_INFO(x, nr)	do { swap_cache_info.x += (nr); } while (0)
 
 static struct {
 	unsigned long add_total;
@@ -78,25 +79,32 @@ void show_swap_cache_info(void)
  */
 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 {
-	int error;
+	int error, i, nr = hpage_nr_pages(page);
 	struct address_space *address_space;
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageSwapCache(page), page);
 	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 
-	get_page(page);
+	page_ref_add(page, nr);
 	SetPageSwapCache(page);
-	set_page_private(page, entry.val);
 
 	address_space = swap_address_space(entry);
 	spin_lock_irq(&address_space->tree_lock);
-	error = radix_tree_insert(&address_space->page_tree,
-					entry.val, page);
+	for (i = 0; i < nr; i++) {
+		struct page *cur_page = page + i;
+		unsigned long index = entry.val + i;
+
+		set_page_private(cur_page, index);
+		error = radix_tree_insert(&address_space->page_tree,
+					  index, cur_page);
+		if (unlikely(error))
+			break;
+	}
 	if (likely(!error)) {
-		address_space->nrpages++;
-		__inc_node_page_state(page, NR_FILE_PAGES);
-		INC_CACHE_INFO(add_total);
+		address_space->nrpages += nr;
+		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
+		ADD_CACHE_INFO(add_total, nr);
 	}
 	spin_unlock_irq(&address_space->tree_lock);
 
@@ -107,9 +115,16 @@ int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 		 * So add_to_swap_cache() doesn't returns -EEXIST.
 		 */
 		VM_BUG_ON(error == -EEXIST);
-		set_page_private(page, 0UL);
 		ClearPageSwapCache(page);
-		put_page(page);
+		set_page_private(page + i, 0UL);
+		while (i--) {
+			struct page *cur_page = page + i;
+			unsigned long index = entry.val + i;
+
+			set_page_private(cur_page, 0UL);
+			radix_tree_delete(&address_space->page_tree, index);
+		}
+		page_ref_sub(page, nr);
 	}
 
 	return error;
@@ -120,7 +135,7 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 {
 	int error;
 
-	error = radix_tree_maybe_preload(gfp_mask);
+	error = radix_tree_maybe_preload_order(gfp_mask, compound_order(page));
 	if (!error) {
 		error = __add_to_swap_cache(page, entry);
 		radix_tree_preload_end();
@@ -136,6 +151,7 @@ void __delete_from_swap_cache(struct page *page)
 {
 	swp_entry_t entry;
 	struct address_space *address_space;
+	int i, nr = hpage_nr_pages(page);
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
@@ -143,12 +159,17 @@ void __delete_from_swap_cache(struct page *page)
 
 	entry.val = page_private(page);
 	address_space = swap_address_space(entry);
-	radix_tree_delete(&address_space->page_tree, page_private(page));
-	set_page_private(page, 0);
 	ClearPageSwapCache(page);
-	address_space->nrpages--;
-	__dec_node_page_state(page, NR_FILE_PAGES);
-	INC_CACHE_INFO(del_total);
+	for (i = 0; i < nr; i++) {
+		struct page *cur_page = page + i;
+
+		radix_tree_delete(&address_space->page_tree,
+				  page_private(cur_page));
+		set_page_private(cur_page, 0);
+	}
+	address_space->nrpages -= nr;
+	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
+	ADD_CACHE_INFO(del_total, nr);
 }
 
 /**
@@ -225,8 +246,8 @@ void delete_from_swap_cache(struct page *page)
 	__delete_from_swap_cache(page);
 	spin_unlock_irq(&address_space->tree_lock);
 
-	swapcache_free(entry);
-	put_page(page);
+	__swapcache_free(entry, PageTransHuge(page));
+	page_ref_sub(page, hpage_nr_pages(page));
 }
 
 /* 
-- 
2.8.1

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#1458946 — [RFC 11/11] mm, THP, swap: Delay splitting THP during swap out

From: Huang Ying <ying.huang@intel.com>

In this patch, the splitting huge page is delayed from almost the first
step of swapping out to after allocating the swap space for THP and
adding the THP into swap cache.  This will reduce lock
acquiring/releasing for locks used for swap space and swap cache
management.

This is the also first step for THP (Transparent Huge Page) swap
support.  The plan is to delaying splitting THP step by step and avoid
splitting THP finally.

The advantages of THP swap support are:

- Batch swap operations for THP to reduce lock acquiring/releasing,
  including allocating/freeing swap space, adding/deleting to/from swap
  cache, and writing/reading swap space, etc.

- THP swap space read/write will be 2M sequence IO.  It is particularly
  helpful for swap read, which usually are 4k random IO.

- It will help memory fragmentation, especially when THP is heavily used
  by the applications.  2M continuous pages will be free up after THP
  swapping out.

With the patchset, the swap out bandwidth improved 12.1% in
vm-scalability swap-w-seq test case with 16 processes on a Xeon E5 v3
system.  To test sequence swap out, the test case uses 16 processes
sequentially allocate and write to anonymous pages until RAM and part of
the swap device is used up.

The detailed compare result is as follow,

base             base+patchset
---------------- --------------------------
         %stddev     %change         %stddev
             \          |                \
   1118821 ±  0%     +12.1%    1254241 ±  1%  vmstat.swap.so
   2460636 ±  1%     +10.6%    2720983 ±  1%  vm-scalability.throughput
    308.79 ±  1%      -7.9%     284.53 ±  1%  vm-scalability.time.elapsed_time
      1639 ±  4%    +232.3%       5446 ±  1%  meminfo.SwapCached
      0.70 ±  3%      +8.7%       0.77 ±  5%  perf-stat.ipc
      9.82 ±  8%     -31.6%       6.72 ±  2%  perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/swap_state.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index a41fd10..5316fbc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -17,6 +17,7 @@
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/migrate.h>
+#include <linux/huge_mm.h>
 
 #include <asm/pgtable.h>
 
@@ -172,12 +173,45 @@ void __delete_from_swap_cache(struct page *page)
 	ADD_CACHE_INFO(del_total, nr);
 }
 
+int add_to_swap_trans_huge(struct page *page, struct list_head *list)
+{
+	swp_entry_t entry;
+	int ret = 0;
+
+	/* cannot split, which may be needed during swap in, skip it */
+	if (!can_split_huge_page(page))
+		return -EBUSY;
+	/* fallback to split huge page firstly if no PMD map */
+	if (!compound_mapcount(page))
+		return 0;
+	entry = get_huge_swap_page();
+	if (!entry.val)
+		return 0;
+	if (mem_cgroup_try_charge_swap(page, entry, HPAGE_PMD_NR)) {
+		__swapcache_free(entry, true);
+		return -EOVERFLOW;
+	}
+	ret = add_to_swap_cache(page, entry,
+				__GFP_HIGH | __GFP_NOMEMALLOC|__GFP_NOWARN);
+	/* -ENOMEM radix-tree allocation failure */
+	if (ret) {
+		__swapcache_free(entry, true);
+		return 0;
+	}
+	ret = split_huge_page_to_list(page, list);
+	if (ret) {
+		delete_from_swap_cache(page);
+		return -EBUSY;
+	}
+	return 1;
+}
+
 /**
  * add_to_swap - allocate swap space for a page
  * @page: page we want to move to swap
  *
  * Allocate swap space for the page and add the page to the
- * swap cache.  Caller needs to hold the page lock. 
+ * swap cache.  Caller needs to hold the page lock.
  */
 int add_to_swap(struct page *page, struct list_head *list)
 {
@@ -187,6 +221,14 @@ int add_to_swap(struct page *page, struct list_head *list)
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageUptodate(page), page);
 
+	if (unlikely(PageTransHuge(page))) {
+		err = add_to_swap_trans_huge(page, list);
+		if (err < 0)
+			return 0;
+		else if (err > 0)
+			return err;
+		/* fallback to split firstly if return 0 */
+	}
 	entry = get_swap_page();
 	if (!entry.val)
 		return 0;
@@ -306,7 +348,7 @@ struct page * lookup_swap_cache(swp_entry_t entry)
 
 	page = find_get_page(swap_address_space(entry), entry.val);
 
-	if (page) {
+	if (page && likely(!PageCompound(page))) {
 		INC_CACHE_INFO(find_success);
 		if (TestClearPageReadahead(page))
 			atomic_inc(&swapin_readahead_hits);
@@ -332,8 +374,13 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		 * that would confuse statistics.
 		 */
 		found_page = find_get_page(swapper_space, entry.val);
-		if (found_page)
+		if (found_page) {
+			if (unlikely(PageCompound(found_page))) {
+				put_page(found_page);
+				found_page = NULL;
+			}
 			break;
+		}
 
 		/*
 		 * Get a new page to read into from swap.
-- 
2.8.1

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#1458954 — [RFC 04/11] mm, memcg: Support to charge/uncharge multiple swap entries

From: Huang Ying <ying.huang@intel.com>

This patch make it possible to charge or uncharge a set of continuous
swap entries in swap cgroup.  The number of swap entries is specified
via an added parameter.

This will be used for THP (Transparent Huge Page) swap support.  Where a
whole swap cluster backing a THP may be allocated and freed as a whole.
So a set of continuous swap entries (512 on x86_64) backing one THP need
to be charged or uncharged together.  This will batch the cgroup
operations for THP swap too.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/swap.h        | 11 +++++----
 include/linux/swap_cgroup.h |  6 +++--
 mm/memcontrol.c             | 54 +++++++++++++++++++++++++--------------------
 mm/shmem.c                  |  2 +-
 mm/swap_cgroup.c            | 17 ++++++++++----
 mm/swap_state.c             |  2 +-
 mm/swapfile.c               |  2 +-
 7 files changed, 57 insertions(+), 37 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index ed41bec..6988bce 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -550,8 +550,9 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 
 #ifdef CONFIG_MEMCG_SWAP
 extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
-extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
-extern void mem_cgroup_uncharge_swap(swp_entry_t entry);
+extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry,
+				      unsigned int nr_entries);
+extern void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_entries);
 extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
 extern bool mem_cgroup_swap_full(struct page *page);
 #else
@@ -560,12 +561,14 @@ static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 }
 
 static inline int mem_cgroup_try_charge_swap(struct page *page,
-					     swp_entry_t entry)
+					     swp_entry_t entry,
+					     unsigned int nr_entries)
 {
 	return 0;
 }
 
-static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
+static inline void mem_cgroup_uncharge_swap(swp_entry_t entry,
+					    unsigned int nr_entries)
 {
 }
 
diff --git a/include/linux/swap_cgroup.h b/include/linux/swap_cgroup.h
index 145306b..b2b8ec7 100644
--- a/include/linux/swap_cgroup.h
+++ b/include/linux/swap_cgroup.h
@@ -7,7 +7,8 @@
 
 extern unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new);
-extern unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id);
+extern unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+					 unsigned int nr_ents);
 extern unsigned short lookup_swap_cgroup_id(swp_entry_t ent);
 extern int swap_cgroup_swapon(int type, unsigned long max_pages);
 extern void swap_cgroup_swapoff(int type);
@@ -15,7 +16,8 @@ extern void swap_cgroup_swapoff(int type);
 #else
 
 static inline
-unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
+unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+				  unsigned int nr_ents)
 {
 	return 0;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1f507f0..d29b368 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2362,10 +2362,9 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 
 #ifdef CONFIG_MEMCG_SWAP
 static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
-					 bool charge)
+				       int nr_entries)
 {
-	int val = (charge) ? 1 : -1;
-	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
+	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], nr_entries);
 }
 
 /**
@@ -2391,8 +2390,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 	new_id = mem_cgroup_id(to);
 
 	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
-		mem_cgroup_swap_statistics(from, false);
-		mem_cgroup_swap_statistics(to, true);
+		mem_cgroup_swap_statistics(from, -1);
+		mem_cgroup_swap_statistics(to, 1);
 		return 0;
 	}
 	return -EINVAL;
@@ -5416,7 +5415,7 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
 		 * let's not wait for it.  The page already received a
 		 * memory+swap charge, drop the swap entry duplicate.
 		 */
-		mem_cgroup_uncharge_swap(entry);
+		mem_cgroup_uncharge_swap(entry, nr_pages);
 	}
 }
 
@@ -5799,9 +5798,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 		return;
 
 	swap_memcg = mem_cgroup_id_get_active(memcg);
-	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg));
+	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg), 1);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(swap_memcg, true);
+	mem_cgroup_swap_statistics(swap_memcg, 1);
 
 	page->mem_cgroup = NULL;
 
@@ -5827,16 +5826,19 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 		css_put(&memcg->css);
 }
 
-/*
- * mem_cgroup_try_charge_swap - try charging a swap entry
+/**
+ * mem_cgroup_try_charge_swap - try charging a set of swap entries
  * @page: page being added to swap
- * @entry: swap entry to charge
+ * @entry: the first swap entry to charge
+ * @nr_entries: the number of swap entries to charge
  *
- * Try to charge @entry to the memcg that @page belongs to.
+ * Try to charge @nr_entries swap entries starting from @entry to the
+ * memcg that @page belongs to.
  *
  * Returns 0 on success, -ENOMEM on failure.
  */
-int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
+int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry,
+			       unsigned int nr_entries)
 {
 	struct mem_cgroup *memcg;
 	struct page_counter *counter;
@@ -5854,25 +5856,29 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 	memcg = mem_cgroup_id_get_active(memcg);
 
 	if (!mem_cgroup_is_root(memcg) &&
-	    !page_counter_try_charge(&memcg->swap, 1, &counter)) {
+	    !page_counter_try_charge(&memcg->swap, nr_entries, &counter)) {
 		mem_cgroup_id_put(memcg);
 		return -ENOMEM;
 	}
 
-	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
+	if (nr_entries > 1)
+		mem_cgroup_id_get_many(memcg, nr_entries - 1);
+	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg), nr_entries);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(memcg, true);
+	mem_cgroup_swap_statistics(memcg, nr_entries);
 
 	return 0;
 }
 
 /**
- * mem_cgroup_uncharge_swap - uncharge a swap entry
- * @entry: swap entry to uncharge
+ * mem_cgroup_uncharge_swap - uncharge a set of swap entries
+ * @entry: the first swap entry to uncharge
+ * @nr_entries: the number of swap entries to uncharge
  *
- * Drop the swap charge associated with @entry.
+ * Drop the swap charge associated with @nr_entries swap entries
+ * starting from @entry.
  */
-void mem_cgroup_uncharge_swap(swp_entry_t entry)
+void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_entries)
 {
 	struct mem_cgroup *memcg;
 	unsigned short id;
@@ -5880,17 +5886,17 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry)
 	if (!do_swap_account)
 		return;
 
-	id = swap_cgroup_record(entry, 0);
+	id = swap_cgroup_record(entry, 0, nr_entries);
 	rcu_read_lock();
 	memcg = mem_cgroup_from_id(id);
 	if (memcg) {
 		if (!mem_cgroup_is_root(memcg)) {
 			if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
-				page_counter_uncharge(&memcg->swap, 1);
+				page_counter_uncharge(&memcg->swap, nr_entries);
 			else
-				page_counter_uncharge(&memcg->memsw, 1);
+				page_counter_uncharge(&memcg->memsw, nr_entries);
 		}
-		mem_cgroup_swap_statistics(memcg, false);
+		mem_cgroup_swap_statistics(memcg, -nr_entries);
 		mem_cgroup_id_put(memcg);
 	}
 	rcu_read_unlock();
diff --git a/mm/shmem.c b/mm/shmem.c
index 7f7748a..fa4067e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1248,7 +1248,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	if (!swap.val)
 		goto redirty;
 
-	if (mem_cgroup_try_charge_swap(page, swap))
+	if (mem_cgroup_try_charge_swap(page, swap, 1))
 		goto free_swap;
 
 	/*
diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index 3563b8b..a2cafbd 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -138,14 +138,16 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 }
 
 /**
- * swap_cgroup_record - record mem_cgroup for this swp_entry.
- * @ent: swap entry to be recorded into
+ * swap_cgroup_record - record mem_cgroup for a set of swap entries
+ * @ent: the first swap entry to be recorded into
  * @id: mem_cgroup to be recorded
+ * @nr_ents: number of swap entries to be recorded
  *
  * Returns old value at success, 0 at failure.
  * (Of course, old value can be 0.)
  */
-unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
+unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+				  unsigned int nr_ents)
 {
 	struct swap_cgroup_iter iter;
 	unsigned short old;
@@ -153,7 +155,14 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
 	swap_cgroup_iter_init(&iter, ent);
 
 	old = iter.sc->id;
-	iter.sc->id = id;
+	for (;;) {
+		VM_BUG_ON(iter.sc->id != old);
+		iter.sc->id = id;
+		nr_ents--;
+		if (!nr_ents)
+			break;
+		swap_cgroup_iter_advance(&iter);
+	}
 
 	swap_cgroup_iter_exit(&iter);
 	return old;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index c8310a3..2013793 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -170,7 +170,7 @@ int add_to_swap(struct page *page, struct list_head *list)
 	if (!entry.val)
 		return 0;
 
-	if (mem_cgroup_try_charge_swap(page, entry)) {
+	if (mem_cgroup_try_charge_swap(page, entry, 1)) {
 		swapcache_free(entry);
 		return 0;
 	}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 18f9292..25363c2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -802,7 +802,7 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
 
 	/* free if no reference */
 	if (!usage) {
-		mem_cgroup_uncharge_swap(entry);
+		mem_cgroup_uncharge_swap(entry, 1);
 		dec_cluster_info_page(p, p->cluster_info, offset);
 		if (offset < p->lowest_bit)
 			p->lowest_bit = offset;
-- 
2.8.1

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#1458955 — [RFC 02/11] swap: Change SWAPFILE_CLUSTER to 512

From: Huang Ying <ying.huang@intel.com>

In this patch, the size of swap cluster is changed to that of THP on
x86_64 (512).  This is for THP (Transparent Huge Page) swap support on
x86_64.  Where one swap cluster will be used to hold the contents of
each THP swapped out.  And some information of the swapped out THP (such
as compound map count) will be recorded in the swap_cluster_info data
structure.

In effect, this will enlarge swap cluster size by 2 times.  Which may
make it harder to find a free cluster when swap space becomes
fragmented.  So that, this may reduce the continuous swap space
allocation and sequence write if that happens in theory.  The
performance test in 0day show no regressions caused by this.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 09e3877..18f9292 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -196,7 +196,7 @@ static void discard_swap_cluster(struct swap_info_struct *si,
 	}
 }
 
-#define SWAPFILE_CLUSTER	256
+#define SWAPFILE_CLUSTER	512
 #define LATENCY_LIMIT		256
 
 static inline void cluster_set_flag(struct swap_cluster_info *info,
-- 
2.8.1

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#1458962 — [RFC 03/11] mm, memcg: Add swap_cgroup_iter iterator

From: Huang Ying <ying.huang@intel.com>

Swap cgroup uses a discontinuous array to store the information for the
swap entries.  lookup_swap_cgroup() provides the good encapsulation to
access one element of the discontinuous array.  To make it easier to
access multiple elements of the discontinuous array, an iterator for
swap cgroup named swap_cgroup_iter is added in this patch.

This will be used for transparent huge page (THP) swap support.  Where
the swap_cgroup for multiple swap entries will be changed together.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/swap_cgroup.c | 62 +++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index 310ac0b..3563b8b 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -18,6 +18,13 @@ struct swap_cgroup {
 };
 #define SC_PER_PAGE	(PAGE_SIZE/sizeof(struct swap_cgroup))
 
+struct swap_cgroup_iter {
+	struct swap_cgroup_ctrl *ctrl;
+	struct swap_cgroup *sc;
+	swp_entry_t entry;
+	unsigned long flags;
+};
+
 /*
  * SwapCgroup implements "lookup" and "exchange" operations.
  * In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
@@ -75,6 +82,34 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 	return sc + offset % SC_PER_PAGE;
 }
 
+static void swap_cgroup_iter_init(struct swap_cgroup_iter *iter, swp_entry_t ent)
+{
+	iter->entry = ent;
+	iter->sc = lookup_swap_cgroup(ent, &iter->ctrl);
+	spin_lock_irqsave(&iter->ctrl->lock, iter->flags);
+}
+
+static void swap_cgroup_iter_exit(struct swap_cgroup_iter *iter)
+{
+	spin_unlock_irqrestore(&iter->ctrl->lock, iter->flags);
+}
+
+/*
+ * swap_cgroup is stored in a kind of discontinuous array.  That is,
+ * they are continuous in one page, but not across page boundary.  And
+ * there is one lock for each page.
+ */
+static void swap_cgroup_iter_advance(struct swap_cgroup_iter *iter)
+{
+	iter->sc++;
+	iter->entry.val++;
+	if (!(((unsigned long)iter->sc) & PAGE_MASK)) {
+		spin_unlock_irqrestore(&iter->ctrl->lock, iter->flags);
+		iter->sc = lookup_swap_cgroup(iter->entry, &iter->ctrl);
+		spin_lock_irqsave(&iter->ctrl->lock, iter->flags);
+	}
+}
+
 /**
  * swap_cgroup_cmpxchg - cmpxchg mem_cgroup's id for this swp_entry.
  * @ent: swap entry to be cmpxchged
@@ -87,20 +122,18 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new)
 {
-	struct swap_cgroup_ctrl *ctrl;
-	struct swap_cgroup *sc;
-	unsigned long flags;
+	struct swap_cgroup_iter iter;
 	unsigned short retval;
 
-	sc = lookup_swap_cgroup(ent, &ctrl);
+	swap_cgroup_iter_init(&iter, ent);
 
-	spin_lock_irqsave(&ctrl->lock, flags);
-	retval = sc->id;
+	retval = iter.sc->id;
 	if (retval == old)
-		sc->id = new;
+		iter.sc->id = new;
 	else
 		retval = 0;
-	spin_unlock_irqrestore(&ctrl->lock, flags);
+
+	swap_cgroup_iter_exit(&iter);
 	return retval;
 }
 
@@ -114,18 +147,15 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
  */
 unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
 {
-	struct swap_cgroup_ctrl *ctrl;
-	struct swap_cgroup *sc;
+	struct swap_cgroup_iter iter;
 	unsigned short old;
-	unsigned long flags;
 
-	sc = lookup_swap_cgroup(ent, &ctrl);
+	swap_cgroup_iter_init(&iter, ent);
 
-	spin_lock_irqsave(&ctrl->lock, flags);
-	old = sc->id;
-	sc->id = id;
-	spin_unlock_irqrestore(&ctrl->lock, flags);
+	old = iter.sc->id;
+	iter.sc->id = id;
 
+	swap_cgroup_iter_exit(&iter);
 	return old;
 }
 
-- 
2.8.1

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#1458964 — [RFC 01/11] swap: Add swap_cluster_list

From: Huang Ying <ying.huang@intel.com>

This is a code clean up patch without functionality changes.  The
swap_cluster_list data structure and its operations is introduced to
provide some better encapsulation for free cluster and discard cluster
list operations.  This avoid some code duplication, improved the code
readability, and reduced the total line number.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/swap.h |  11 +++--
 mm/swapfile.c        | 132 ++++++++++++++++++++++++---------------------------
 2 files changed, 69 insertions(+), 74 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index b17cc48..ed41bec 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -191,6 +191,11 @@ struct percpu_cluster {
 	unsigned int next; /* Likely next allocation offset */
 };
 
+struct swap_cluster_list {
+	struct swap_cluster_info head;
+	struct swap_cluster_info tail;
+};
+
 /*
  * The in-memory structure used to track swap areas.
  */
@@ -203,8 +208,7 @@ struct swap_info_struct {
 	unsigned int	max;		/* extent of the swap_map */
 	unsigned char *swap_map;	/* vmalloc'ed array of usage counts */
 	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
-	struct swap_cluster_info free_cluster_head; /* free cluster list head */
-	struct swap_cluster_info free_cluster_tail; /* free cluster list tail */
+	struct swap_cluster_list free_clusters; /* free clusters list */
 	unsigned int lowest_bit;	/* index of first free in swap_map */
 	unsigned int highest_bit;	/* index of last free in swap_map */
 	unsigned int pages;		/* total of usable pages of swap */
@@ -235,8 +239,7 @@ struct swap_info_struct {
 					 * first.
 					 */
 	struct work_struct discard_work; /* discard worker */
-	struct swap_cluster_info discard_cluster_head; /* list head of discard clusters */
-	struct swap_cluster_info discard_cluster_tail; /* list tail of discard clusters */
+	struct swap_cluster_list discard_clusters; /* discard clusters list */
 };
 
 /* linux/mm/workingset.c */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 78cfa29..09e3877 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -257,6 +257,53 @@ static inline void cluster_set_null(struct swap_cluster_info *info)
 	info->data = 0;
 }
 
+static inline bool cluster_list_empty(struct swap_cluster_list *list)
+{
+	return cluster_is_null(&list->head);
+}
+
+static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
+{
+	return cluster_next(&list->head);
+}
+
+static void cluster_list_init(struct swap_cluster_list *list)
+{
+	cluster_set_null(&list->head);
+	cluster_set_null(&list->tail);
+}
+
+static void cluster_list_add_tail(struct swap_cluster_list *list,
+				  struct swap_cluster_info *ci,
+				  unsigned int idx)
+{
+	if (cluster_list_empty(list)) {
+		cluster_set_next_flag(&list->head, idx, 0);
+		cluster_set_next_flag(&list->tail, idx, 0);
+	} else {
+		unsigned int tail = cluster_next(&list->tail);
+
+		cluster_set_next(&ci[tail], idx);
+		cluster_set_next_flag(&list->tail, idx, 0);
+	}
+}
+
+static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
+					   struct swap_cluster_info *ci)
+{
+	unsigned int idx;
+
+	idx = cluster_next(&list->head);
+	if (cluster_next(&list->tail) == idx) {
+		cluster_set_null(&list->head);
+		cluster_set_null(&list->tail);
+	} else
+		cluster_set_next_flag(&list->head,
+				      cluster_next(&ci[idx]), 0);
+
+	return idx;
+}
+
 /* Add a cluster to discard list and schedule it to do discard */
 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
 		unsigned int idx)
@@ -270,17 +317,7 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
 	memset(si->swap_map + idx * SWAPFILE_CLUSTER,
 			SWAP_MAP_BAD, SWAPFILE_CLUSTER);
 
-	if (cluster_is_null(&si->discard_cluster_head)) {
-		cluster_set_next_flag(&si->discard_cluster_head,
-						idx, 0);
-		cluster_set_next_flag(&si->discard_cluster_tail,
-						idx, 0);
-	} else {
-		unsigned int tail = cluster_next(&si->discard_cluster_tail);
-		cluster_set_next(&si->cluster_info[tail], idx);
-		cluster_set_next_flag(&si->discard_cluster_tail,
-						idx, 0);
-	}
+	cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
 
 	schedule_work(&si->discard_work);
 }
@@ -296,15 +333,8 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
 
 	info = si->cluster_info;
 
-	while (!cluster_is_null(&si->discard_cluster_head)) {
-		idx = cluster_next(&si->discard_cluster_head);
-
-		cluster_set_next_flag(&si->discard_cluster_head,
-						cluster_next(&info[idx]), 0);
-		if (cluster_next(&si->discard_cluster_tail) == idx) {
-			cluster_set_null(&si->discard_cluster_head);
-			cluster_set_null(&si->discard_cluster_tail);
-		}
+	while (!cluster_list_empty(&si->discard_clusters)) {
+		idx = cluster_list_del_first(&si->discard_clusters, info);
 		spin_unlock(&si->lock);
 
 		discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
@@ -312,19 +342,7 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
 
 		spin_lock(&si->lock);
 		cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
-		if (cluster_is_null(&si->free_cluster_head)) {
-			cluster_set_next_flag(&si->free_cluster_head,
-						idx, 0);
-			cluster_set_next_flag(&si->free_cluster_tail,
-						idx, 0);
-		} else {
-			unsigned int tail;
-
-			tail = cluster_next(&si->free_cluster_tail);
-			cluster_set_next(&info[tail], idx);
-			cluster_set_next_flag(&si->free_cluster_tail,
-						idx, 0);
-		}
+		cluster_list_add_tail(&si->free_clusters, info, idx);
 		memset(si->swap_map + idx * SWAPFILE_CLUSTER,
 				0, SWAPFILE_CLUSTER);
 	}
@@ -353,13 +371,8 @@ static void inc_cluster_info_page(struct swap_info_struct *p,
 	if (!cluster_info)
 		return;
 	if (cluster_is_free(&cluster_info[idx])) {
-		VM_BUG_ON(cluster_next(&p->free_cluster_head) != idx);
-		cluster_set_next_flag(&p->free_cluster_head,
-			cluster_next(&cluster_info[idx]), 0);
-		if (cluster_next(&p->free_cluster_tail) == idx) {
-			cluster_set_null(&p->free_cluster_tail);
-			cluster_set_null(&p->free_cluster_head);
-		}
+		VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx);
+		cluster_list_del_first(&p->free_clusters, cluster_info);
 		cluster_set_count_flag(&cluster_info[idx], 0, 0);
 	}
 
@@ -398,14 +411,7 @@ static void dec_cluster_info_page(struct swap_info_struct *p,
 		}
 
 		cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
-		if (cluster_is_null(&p->free_cluster_head)) {
-			cluster_set_next_flag(&p->free_cluster_head, idx, 0);
-			cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
-		} else {
-			unsigned int tail = cluster_next(&p->free_cluster_tail);
-			cluster_set_next(&cluster_info[tail], idx);
-			cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
-		}
+		cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
 	}
 }
 
@@ -421,8 +427,8 @@ scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
 	bool conflict;
 
 	offset /= SWAPFILE_CLUSTER;
-	conflict = !cluster_is_null(&si->free_cluster_head) &&
-		offset != cluster_next(&si->free_cluster_head) &&
+	conflict = !cluster_list_empty(&si->free_clusters) &&
+		offset != cluster_list_first(&si->free_clusters) &&
 		cluster_is_free(&si->cluster_info[offset]);
 
 	if (!conflict)
@@ -447,11 +453,11 @@ static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
 new_cluster:
 	cluster = this_cpu_ptr(si->percpu_cluster);
 	if (cluster_is_null(&cluster->index)) {
-		if (!cluster_is_null(&si->free_cluster_head)) {
-			cluster->index = si->free_cluster_head;
+		if (!cluster_list_empty(&si->free_clusters)) {
+			cluster->index = si->free_clusters.head;
 			cluster->next = cluster_next(&cluster->index) *
 					SWAPFILE_CLUSTER;
-		} else if (!cluster_is_null(&si->discard_cluster_head)) {
+		} else if (!cluster_list_empty(&si->discard_clusters)) {
 			/*
 			 * we don't have free cluster but have some clusters in
 			 * discarding, do discard now and reclaim them
@@ -2292,10 +2298,8 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 
 	nr_good_pages = maxpages - 1;	/* omit header page */
 
-	cluster_set_null(&p->free_cluster_head);
-	cluster_set_null(&p->free_cluster_tail);
-	cluster_set_null(&p->discard_cluster_head);
-	cluster_set_null(&p->discard_cluster_tail);
+	cluster_list_init(&p->free_clusters);
+	cluster_list_init(&p->discard_clusters);
 
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
 		unsigned int page_nr = swap_header->info.badpages[i];
@@ -2341,19 +2345,7 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 	for (i = 0; i < nr_clusters; i++) {
 		if (!cluster_count(&cluster_info[idx])) {
 			cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
-			if (cluster_is_null(&p->free_cluster_head)) {
-				cluster_set_next_flag(&p->free_cluster_head,
-								idx, 0);
-				cluster_set_next_flag(&p->free_cluster_tail,
-								idx, 0);
-			} else {
-				unsigned int tail;
-
-				tail = cluster_next(&p->free_cluster_tail);
-				cluster_set_next(&cluster_info[tail], idx);
-				cluster_set_next_flag(&p->free_cluster_tail,
-								idx, 0);
-			}
+			cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
 		}
 		idx++;
 		if (idx == nr_clusters)
-- 
2.8.1

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#1458967 — [RFC 06/11] mm, THP, swap: Add get_huge_swap_page()

From: Huang Ying <ying.huang@intel.com>

A variation of get_swap_page(), get_huge_swap_page(), is added to
allocate a swap cluster (512 swap slots) based on the swap cluster
allocation function.  A fair simple algorithm is used, that is, only the
first swap device in priority list will be tried to allocate the swap
cluster.  The function will fail if that trying is not successful, and
the caller will fall back to allocate single swap slot instead.  This
works good enough for normal cases.

This will be used for THP (Transparent Huge Page) swap support.  Where
get_huge_swap_page() will be used to allocate one swap cluster for each
THP swapped out.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/swap.h | 21 ++++++++++++++++++++-
 mm/swapfile.c        | 29 +++++++++++++++++++++++------
 2 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 6988bce..95a526e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -399,7 +399,7 @@ static inline long get_nr_swap_pages(void)
 }
 
 extern void si_swapinfo(struct sysinfo *);
-extern swp_entry_t get_swap_page(void);
+extern swp_entry_t __get_swap_page(bool huge);
 extern swp_entry_t get_swap_page_of_type(int);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 extern void swap_shmem_alloc(swp_entry_t);
@@ -419,6 +419,20 @@ extern bool reuse_swap_page(struct page *, int *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
 
+static inline swp_entry_t get_swap_page(void)
+{
+	return __get_swap_page(false);
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+extern swp_entry_t get_huge_swap_page(void);
+#else
+static inline swp_entry_t get_huge_swap_page(void)
+{
+	return (swp_entry_t) {0};
+}
+#endif
+
 #else /* CONFIG_SWAP */
 
 #define swap_address_space(entry)		(NULL)
@@ -525,6 +539,11 @@ static inline swp_entry_t get_swap_page(void)
 	return entry;
 }
 
+static inline swp_entry_t get_huge_swap_page(void)
+{
+	return (swp_entry_t) {0};
+}
+
 #endif /* CONFIG_SWAP */
 
 #ifdef CONFIG_MEMCG
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d710e0e..5cd78c7 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -747,14 +747,15 @@ static unsigned long swap_alloc_huge_cluster(struct swap_info_struct *si)
 	return offset;
 }
 
-swp_entry_t get_swap_page(void)
+swp_entry_t __get_swap_page(bool huge)
 {
 	struct swap_info_struct *si, *next;
 	pgoff_t offset;
+	int nr_pages = huge_cluster_nr_entries(huge);
 
-	if (atomic_long_read(&nr_swap_pages) <= 0)
+	if (atomic_long_read(&nr_swap_pages) < nr_pages)
 		goto noswap;
-	atomic_long_dec(&nr_swap_pages);
+	atomic_long_sub(nr_pages, &nr_swap_pages);
 
 	spin_lock(&swap_avail_lock);
 
@@ -782,10 +783,15 @@ start_over:
 		}
 
 		/* This is called for allocating swap entry for cache */
-		offset = scan_swap_map(si, SWAP_HAS_CACHE);
+		if (likely(nr_pages == 1))
+			offset = scan_swap_map(si, SWAP_HAS_CACHE);
+		else
+			offset = swap_alloc_huge_cluster(si);
 		spin_unlock(&si->lock);
 		if (offset)
 			return swp_entry(si->type, offset);
+		else if (unlikely(nr_pages != 1))
+			goto fail_alloc;
 		pr_debug("scan_swap_map of si %d failed to find offset\n",
 		       si->type);
 		spin_lock(&swap_avail_lock);
@@ -805,12 +811,23 @@ nextsi:
 	}
 
 	spin_unlock(&swap_avail_lock);
-
-	atomic_long_inc(&nr_swap_pages);
+fail_alloc:
+	atomic_long_add(nr_pages, &nr_swap_pages);
 noswap:
 	return (swp_entry_t) {0};
 }
 
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+swp_entry_t get_huge_swap_page(void)
+{
+	if (SWAPFILE_CLUSTER != HPAGE_PMD_NR)
+		return (swp_entry_t) {0};
+
+	return __get_swap_page(true);
+}
+#endif
+
 /* The only caller of this function is now suspend routine */
 swp_entry_t get_swap_page_of_type(int type)
 {
-- 
2.8.1

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#1458968 — [RFC 05/11] mm, THP, swap: Add swap cluster allocate/free functions

From: Huang Ying <ying.huang@intel.com>

The swap cluster allocation/free functions are added based on the
existing swap cluster management mechanism for SSD.  These functions
don't work for traditional hard disk because the existing swap cluster
management mechanism doesn't work for it.  The hard disk support may be
added if someone really need that.  But that needn't be included in this
patchset.

This will be used for THP (Transparent Huge Page) swap support.  Where
one swap cluster will hold the contents of each THP swapped out.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/swapfile.c | 194 +++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 137 insertions(+), 57 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 25363c2..d710e0e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -322,6 +322,14 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
 	schedule_work(&si->discard_work);
 }
 
+static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
+{
+	struct swap_cluster_info *ci = si->cluster_info;
+
+	cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
+	cluster_list_add_tail(&si->free_clusters, ci, idx);
+}
+
 /*
  * Doing discard actually. After a cluster discard is finished, the cluster
  * will be added to free cluster list. caller should hold si->lock.
@@ -341,8 +349,7 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
 				SWAPFILE_CLUSTER);
 
 		spin_lock(&si->lock);
-		cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
-		cluster_list_add_tail(&si->free_clusters, info, idx);
+		__free_cluster(si, idx);
 		memset(si->swap_map + idx * SWAPFILE_CLUSTER,
 				0, SWAPFILE_CLUSTER);
 	}
@@ -359,6 +366,34 @@ static void swap_discard_work(struct work_struct *work)
 	spin_unlock(&si->lock);
 }
 
+static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
+{
+	struct swap_cluster_info *ci = si->cluster_info;
+
+	VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
+	cluster_list_del_first(&si->free_clusters, ci);
+	cluster_set_count_flag(ci + idx, 0, 0);
+}
+
+static void free_cluster(struct swap_info_struct *si, unsigned long idx)
+{
+	struct swap_cluster_info *ci = si->cluster_info + idx;
+
+	VM_BUG_ON(cluster_count(ci) != 0);
+	/*
+	 * If the swap is discardable, prepare discard the cluster
+	 * instead of free it immediately. The cluster will be freed
+	 * after discard.
+	 */
+	if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
+	    (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
+		swap_cluster_schedule_discard(si, idx);
+		return;
+	}
+
+	__free_cluster(si, idx);
+}
+
 /*
  * The cluster corresponding to page_nr will be used. The cluster will be
  * removed from free cluster list and its usage counter will be increased.
@@ -370,11 +405,8 @@ static void inc_cluster_info_page(struct swap_info_struct *p,
 
 	if (!cluster_info)
 		return;
-	if (cluster_is_free(&cluster_info[idx])) {
-		VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx);
-		cluster_list_del_first(&p->free_clusters, cluster_info);
-		cluster_set_count_flag(&cluster_info[idx], 0, 0);
-	}
+	if (cluster_is_free(&cluster_info[idx]))
+		alloc_cluster(p, idx);
 
 	VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
 	cluster_set_count(&cluster_info[idx],
@@ -398,21 +430,8 @@ static void dec_cluster_info_page(struct swap_info_struct *p,
 	cluster_set_count(&cluster_info[idx],
 		cluster_count(&cluster_info[idx]) - 1);
 
-	if (cluster_count(&cluster_info[idx]) == 0) {
-		/*
-		 * If the swap is discardable, prepare discard the cluster
-		 * instead of free it immediately. The cluster will be freed
-		 * after discard.
-		 */
-		if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
-				 (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
-			swap_cluster_schedule_discard(p, idx);
-			return;
-		}
-
-		cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
-		cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
-	}
+	if (cluster_count(&cluster_info[idx]) == 0)
+		free_cluster(p, idx);
 }
 
 /*
@@ -493,6 +512,68 @@ new_cluster:
 	*scan_base = tmp;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline unsigned int huge_cluster_nr_entries(bool huge)
+{
+	return huge ? SWAPFILE_CLUSTER : 1;
+}
+#else
+#define huge_cluster_nr_entries(huge)	1
+#endif
+
+static void __swap_entry_alloc(struct swap_info_struct *si, unsigned long offset,
+			       bool huge)
+{
+	unsigned int nr_entries = huge_cluster_nr_entries(huge);
+	unsigned int end = offset + nr_entries - 1;
+
+	if (offset == si->lowest_bit)
+		si->lowest_bit += nr_entries;
+	if (end == si->highest_bit)
+		si->highest_bit -= nr_entries;
+	si->inuse_pages += nr_entries;
+	if (si->inuse_pages == si->pages) {
+		si->lowest_bit = si->max;
+		si->highest_bit = 0;
+		spin_lock(&swap_avail_lock);
+		plist_del(&si->avail_list, &swap_avail_head);
+		spin_unlock(&swap_avail_lock);
+	}
+}
+
+static void __swap_entry_free(struct swap_info_struct *si, unsigned long offset,
+			      bool huge)
+{
+	unsigned int nr_entries = huge_cluster_nr_entries(huge);
+	unsigned long end = offset + nr_entries - 1;
+	void (*swap_slot_free_notify)(struct block_device *, unsigned long);
+
+	if (offset < si->lowest_bit)
+		si->lowest_bit = offset;
+	if (end > si->highest_bit) {
+		bool was_full = !si->highest_bit;
+
+		si->highest_bit = end;
+		if (was_full && (si->flags & SWP_WRITEOK)) {
+			spin_lock(&swap_avail_lock);
+			WARN_ON(!plist_node_empty(&si->avail_list));
+			if (plist_node_empty(&si->avail_list))
+				plist_add(&si->avail_list, &swap_avail_head);
+			spin_unlock(&swap_avail_lock);
+		}
+	}
+	atomic_long_add(nr_entries, &nr_swap_pages);
+	si->inuse_pages -= nr_entries;
+	if (si->flags & SWP_BLKDEV)
+		swap_slot_free_notify = si->bdev->bd_disk->fops->swap_slot_free_notify;
+	while (offset <= end) {
+		frontswap_invalidate_page(si->type, offset);
+		if (swap_slot_free_notify)
+			swap_slot_free_notify(si->bdev, offset);
+		offset++;
+	}
+}
+
 static unsigned long scan_swap_map(struct swap_info_struct *si,
 				   unsigned char usage)
 {
@@ -587,18 +668,7 @@ checks:
 	if (si->swap_map[offset])
 		goto scan;
 
-	if (offset == si->lowest_bit)
-		si->lowest_bit++;
-	if (offset == si->highest_bit)
-		si->highest_bit--;
-	si->inuse_pages++;
-	if (si->inuse_pages == si->pages) {
-		si->lowest_bit = si->max;
-		si->highest_bit = 0;
-		spin_lock(&swap_avail_lock);
-		plist_del(&si->avail_list, &swap_avail_head);
-		spin_unlock(&swap_avail_lock);
-	}
+	__swap_entry_alloc(si, offset, false);
 	si->swap_map[offset] = usage;
 	inc_cluster_info_page(si, si->cluster_info, offset);
 	si->cluster_next = offset + 1;
@@ -645,6 +715,38 @@ no_page:
 	return 0;
 }
 
+static void swap_free_huge_cluster(struct swap_info_struct *si, unsigned long idx)
+{
+	struct swap_cluster_info *ci = si->cluster_info + idx;
+	unsigned long offset = idx * SWAPFILE_CLUSTER;
+
+	cluster_set_count_flag(ci, 0, 0);
+	free_cluster(si, idx);
+	__swap_entry_free(si, offset, true);
+}
+
+static unsigned long swap_alloc_huge_cluster(struct swap_info_struct *si)
+{
+	unsigned long idx;
+	struct swap_cluster_info *ci;
+	unsigned long offset, i;
+	unsigned char *map;
+
+	if (cluster_list_empty(&si->free_clusters))
+		return 0;
+	idx = cluster_list_first(&si->free_clusters);
+	alloc_cluster(si, idx);
+	ci = si->cluster_info + idx;
+	cluster_set_count_flag(ci, SWAPFILE_CLUSTER, 0);
+
+	offset = idx * SWAPFILE_CLUSTER;
+	__swap_entry_alloc(si, offset, true);
+	map = si->swap_map + offset;
+	for (i = 0; i < SWAPFILE_CLUSTER; i++)
+		map[i] = SWAP_HAS_CACHE;
+	return offset;
+}
+
 swp_entry_t get_swap_page(void)
 {
 	struct swap_info_struct *si, *next;
@@ -804,29 +906,7 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
 	if (!usage) {
 		mem_cgroup_uncharge_swap(entry, 1);
 		dec_cluster_info_page(p, p->cluster_info, offset);
-		if (offset < p->lowest_bit)
-			p->lowest_bit = offset;
-		if (offset > p->highest_bit) {
-			bool was_full = !p->highest_bit;
-			p->highest_bit = offset;
-			if (was_full && (p->flags & SWP_WRITEOK)) {
-				spin_lock(&swap_avail_lock);
-				WARN_ON(!plist_node_empty(&p->avail_list));
-				if (plist_node_empty(&p->avail_list))
-					plist_add(&p->avail_list,
-						  &swap_avail_head);
-				spin_unlock(&swap_avail_lock);
-			}
-		}
-		atomic_long_inc(&nr_swap_pages);
-		p->inuse_pages--;
-		frontswap_invalidate_page(p->type, offset);
-		if (p->flags & SWP_BLKDEV) {
-			struct gendisk *disk = p->bdev->bd_disk;
-			if (disk->fops->swap_slot_free_notify)
-				disk->fops->swap_slot_free_notify(p->bdev,
-								  offset);
-		}
+		__swap_entry_free(p, offset, false);
 	}
 
 	return usage;
-- 
2.8.1

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#1459022

Hi, All,

"Huang, Ying" <ying.huang@intel.com> writes:

> From: Huang Ying <ying.huang@intel.com>
>
> This patchset is based on 8/4 head of mmotm/master.
>
> This is the first step for Transparent Huge Page (THP) swap support.
> The plan is to delaying splitting THP step by step and avoid splitting
> THP finally during THP swapping out and swapping in.
>
> The advantages of THP swap support are:
>
> - Batch swap operations for THP to reduce lock acquiring/releasing,
>   including allocating/freeing swap space, adding/deleting to/from swap
>   cache, and writing/reading swap space, etc.
>
> - THP swap space read/write will be 2M sequence IO.  It is particularly
>   helpful for swap read, which usually are 4k random IO.
>
> - It will help memory fragmentation, especially when THP is heavily used
>   by the applications.  2M continuous pages will be free up after THP
>   swapping out.
>
> As the first step, in this patchset, the splitting huge page is
> delayed from almost the first step of swapping out to after allocating
> the swap space for THP and adding the THP into swap cache.  This will
> reduce lock acquiring/releasing for locks used for swap space and swap
> cache management.

For this patchset posting,

In general, I want to check the basic design with memory management
subsystem maintainers and developers.

For [RFC 01/11] swap: Add swap_cluster_list, it is a cleanup patch.  And
I think it should be useful independently.

I am not very confident about the memcg part, that is

[RFC 03/11] mm, memcg: Add swap_cgroup_iter iterator
[RFC 04/11] mm, memcg: Support to charge/uncharge multiple swap entries

Please help me to check it.

Best Regards,
Huang, Ying

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