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[PATCH V4 6/6] proc: show MADV_FREE pages info in smaps

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  [PATCH V4 6/6] proc: show MADV_FREE pages info in smaps Shaohua Li <shli@fb.com> - 2017-02-22 20:00 +0100
    Re: [PATCH V4 6/6] proc: show MADV_FREE pages info in smaps Johannes Weiner <hannes@cmpxchg.org> - 2017-02-23 17:30 +0100
    Re: [PATCH V4 6/6] proc: show MADV_FREE pages info in smaps Minchan Kim <minchan@kernel.org> - 2017-02-24 03:20 +0100
    Re: [PATCH V4 6/6] proc: show MADV_FREE pages info in smaps Dave Hansen <dave.hansen@intel.com> - 2017-02-24 18:10 +0100

#1586408 — [PATCH V4 6/6] proc: show MADV_FREE pages info in smaps

show MADV_FREE pages info of each vma in smaps. The interface is for
diganose or monitoring purpose, userspace could use it to understand
what happens in the application. Since userspace could dirty MADV_FREE
pages without notice from kernel, this interface is the only place we
can get accurate accounting info about MADV_FREE pages.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Shaohua Li <shli@fb.com>
---
 Documentation/filesystems/proc.txt | 4 ++++
 fs/proc/task_mmu.c                 | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index c94b467..45853e1 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -412,6 +412,7 @@ Private_Clean:         0 kB
 Private_Dirty:         0 kB
 Referenced:          892 kB
 Anonymous:             0 kB
+LazyFree:              0 kB
 AnonHugePages:         0 kB
 ShmemPmdMapped:        0 kB
 Shared_Hugetlb:        0 kB
@@ -441,6 +442,9 @@ accessed.
 "Anonymous" shows the amount of memory that does not belong to any file.  Even
 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 and a page is modified, the file page is replaced by a private anonymous copy.
+"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
+The memory isn't freed immediately with madvise(). It's freed in memory
+pressure if the memory is clean.
 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
 huge pages.
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ee3efb2..8a5ec00 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -440,6 +440,7 @@ struct mem_size_stats {
 	unsigned long private_dirty;
 	unsigned long referenced;
 	unsigned long anonymous;
+	unsigned long lazyfree;
 	unsigned long anonymous_thp;
 	unsigned long shmem_thp;
 	unsigned long swap;
@@ -456,8 +457,11 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
 	int i, nr = compound ? 1 << compound_order(page) : 1;
 	unsigned long size = nr * PAGE_SIZE;
 
-	if (PageAnon(page))
+	if (PageAnon(page)) {
 		mss->anonymous += size;
+		if (!PageSwapBacked(page) && !dirty && !PageDirty(page))
+			mss->lazyfree += size;
+	}
 
 	mss->resident += size;
 	/* Accumulate the size in pages that have been accessed. */
@@ -770,6 +774,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 		   "Private_Dirty:  %8lu kB\n"
 		   "Referenced:     %8lu kB\n"
 		   "Anonymous:      %8lu kB\n"
+		   "LazyFree:       %8lu kB\n"
 		   "AnonHugePages:  %8lu kB\n"
 		   "ShmemPmdMapped: %8lu kB\n"
 		   "Shared_Hugetlb: %8lu kB\n"
@@ -788,6 +793,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 		   mss.private_dirty >> 10,
 		   mss.referenced >> 10,
 		   mss.anonymous >> 10,
+		   mss.lazyfree >> 10,
 		   mss.anonymous_thp >> 10,
 		   mss.shmem_thp >> 10,
 		   mss.shared_hugetlb >> 10,
-- 
2.9.3

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#1587000

On Wed, Feb 22, 2017 at 10:50:44AM -0800, Shaohua Li wrote:
> show MADV_FREE pages info of each vma in smaps. The interface is for
> diganose or monitoring purpose, userspace could use it to understand
> what happens in the application. Since userspace could dirty MADV_FREE
> pages without notice from kernel, this interface is the only place we
> can get accurate accounting info about MADV_FREE pages.
> 
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Shaohua Li <shli@fb.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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#1587241

On Wed, Feb 22, 2017 at 10:50:44AM -0800, Shaohua Li wrote:
> show MADV_FREE pages info of each vma in smaps. The interface is for
> diganose or monitoring purpose, userspace could use it to understand
> what happens in the application. Since userspace could dirty MADV_FREE
> pages without notice from kernel, this interface is the only place we
> can get accurate accounting info about MADV_FREE pages.
> 
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Shaohua Li <shli@fb.com>
Acked-by: Minchan Kim <minchan@kernel.org>

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#1587807

On 02/22/2017 10:50 AM, Shaohua Li wrote:
> @@ -770,6 +774,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
>  		   "Private_Dirty:  %8lu kB\n"
>  		   "Referenced:     %8lu kB\n"
>  		   "Anonymous:      %8lu kB\n"
> +		   "LazyFree:       %8lu kB\n"
>  		   "AnonHugePages:  %8lu kB\n"
>  		   "ShmemPmdMapped: %8lu kB\n"
>  		   "Shared_Hugetlb: %8lu kB\n"

I've been as guily of this in the past as anyone, but are we just going
to keep adding fields to smaps forever?  For the vast, vast, majority of
folks, this will simply waste the 21 bytes * nr_vmas that it costs us to
print "LazyFree:       0 kB\n" over and over.

Should we maybe start a habit of not printing an entry when it's "0 kB"?

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