+ mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch added to -mm tree

* + mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch added to -mm tree
@ 2020-12-23  2:23 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2020-12-23  2:23 UTC (permalink / raw)
  To: mm-commits, vdavydov.dev, shakeelb, samitolvanen, rdunlap,
	rafael, pankaj.gupta, neilb, mhocko, iamjoonsoo.kim, hughd,
	hannes, guro, gregkh, feng.tang, adobriyan, songmuchun


The patch titled
     Subject: mm: memcontrol: fix NR_ANON_THPS accounting in charge moving
has been added to the -mm tree.  Its filename is
     mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: memcontrol: fix NR_ANON_THPS accounting in charge moving

Patch series "Convert all THP vmstat counters to pages", v5.

This patch series is aimed to convert all THP vmstat counters to pages.

The unit of some vmstat counters are pages, some are bytes, some are
HPAGE_PMD_NR, and some are KiB.  When we want to expose these vmstat
counters to the userspace, we have to know the unit of the vmstat counters
is which one.  When the unit is bytes or kB, both clearly distinguishable
by the B/KB suffix.  But for the THP vmstat counters, we may make
mistakes.

For example, the below is some bug fix for the THP vmstat counters:

  - 7de2e9f195b9 ("mm: memcontrol: correct the NR_ANON_THPS counter of hierarchical memcg")
  - The first commit in this series ("fix NR_ANON_THPS accounting in charge moving")

This patch series can make the code clear.  And make all the unit of the
THP vmstat counters in pages.  Finally, the unit of the vmstat counters
are pages, kB and bytes.  The B/KB suffix can tell us that the unit is
bytes or kB.  The rest which is without suffix are pages.

In this series, I changed the following vmstat counters unit from
HPAGE_PMD_NR to pages.  However, there is no change to the print format of
output to user space.

  - NR_ANON_THPS
  - NR_FILE_THPS
  - NR_SHMEM_THPS
  - NR_SHMEM_PMDMAPPED
  - NR_FILE_PMDMAPPED

Doing this also can make the statistics more accuracy for the THP vmstat
counters.  This series is consistent with 8f182270dfec ("mm/swap.c: flush
lru pvecs on compound page arrival").

Because we use struct per_cpu_nodestat to cache the vmstat counters, which
leads to inaccurate statistics expecially THP vmstat counters.  In the
systems with hundreads of processors it can be GBs of memory.  For
example, for a 96 CPUs system, the threshold is the maximum number of 125.
And the per cpu counters can cache 23.4375 GB in total.

The THP page is already a form of batched addition (it will add 512 worth
of memory in one go) so skipping the batching seems like sensible. 
Although every THP stats update overflows the per-cpu counter, resorting
to atomic global updates.  But it can make the statistics more accuracy
for the THP vmstat counters.  From this point of view, I think that do
this converting is reasonable.

Thanks Hugh for mentioning this.  This was inspired by Johannes and Roman.
Thanks to them.


This patch (of 7):

The unit of NR_ANON_THPS is HPAGE_PMD_NR already.  So it should inc/dec by
one rather than nr_pages.

Link: https://lkml.kernel.org/r/20201217034356.4708-1-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20201217034356.4708-2-songmuchun@bytedance.com
Fixes: 468c398233da ("mm: memcontrol: switch to native NR_ANON_THPS counter")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael. J. Wysocki <rafael@kernel.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/memcontrol.c~mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving
+++ a/mm/memcontrol.c
@@ -5654,10 +5654,8 @@ static int mem_cgroup_move_account(struc
 			__mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
 			__mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
 			if (PageTransHuge(page)) {
-				__mod_lruvec_state(from_vec, NR_ANON_THPS,
-						   -nr_pages);
-				__mod_lruvec_state(to_vec, NR_ANON_THPS,
-						   nr_pages);
+				__dec_lruvec_state(from_vec, NR_ANON_THPS);
+				__inc_lruvec_state(to_vec, NR_ANON_THPS);
 			}
 
 		}
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch
mm-memcontrol-convert-nr_anon_thps-account-to-pages.patch
mm-memcontrol-convert-nr_file_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_pmdmapped-account-to-pages.patch
mm-memcontrol-convert-nr_file_pmdmapped-account-to-pages.patch
mm-memcontrol-make-the-slab-calculation-consistent.patch


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