The patch titled
Subject: mm: memcg: fix swapcached stat accounting
has been added to the -mm mm-unstable branch. Its filename is
mm-memcg-fix-swapcached-stat-accounting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-fix-swapcached-stat-accounting.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm: memcg: fix swapcached stat accounting
Date: Sun, 4 Dec 2022 17:01:03 -0800 (PST)
I'd been worried by high "swapcached" counts in memcg OOM reports, thought
we had a problem freeing swapcache, but it was just the accounting that
was wrong.
Two issues:
1. When __remove_mapping() removes swapcache,
__delete_from_swap_cache() relies on memcg_data for the right counts to
be updated; but that had already been reset by mem_cgroup_swapout().
Swap those calls around - mem_cgroup_swapout() does not require the
swapcached flag to be set.
6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal
implementation") already made a similar swap for workingset_eviction(),
but not for this.
2. memcg's "swapcached" count was added for memcg v2 stats, but
displayed on OOM even for memcg v1: so mem_cgroup_move_account() ought
to move it.
Link: https://lkml.kernel.org/r/b8b96ee0-1e1e-85f8-df97-c82a11d7cd14@xxxxxxxxxx
Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 6 ++++++
mm/vmscan.c | 3 +--
2 files changed, 7 insertions(+), 2 deletions(-)
--- a/mm/memcontrol.c~mm-memcg-fix-swapcached-stat-accounting
+++ a/mm/memcontrol.c
@@ -5756,6 +5756,12 @@ static int mem_cgroup_move_account(struc
}
}
+#ifdef CONFIG_SWAP
+ if (folio_test_swapcache(folio)) {
+ __mod_lruvec_state(from_vec, NR_SWAPCACHE, -nr_pages);
+ __mod_lruvec_state(to_vec, NR_SWAPCACHE, nr_pages);
+ }
+#endif
if (folio_test_writeback(folio)) {
__mod_lruvec_state(from_vec, NR_WRITEBACK, -nr_pages);
__mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages);
--- a/mm/vmscan.c~mm-memcg-fix-swapcached-stat-accounting
+++ a/mm/vmscan.c
@@ -1368,11 +1368,10 @@ static int __remove_mapping(struct addre
if (folio_test_swapcache(folio)) {
swp_entry_t swap = folio_swap_entry(folio);
- /* get a shadow entry before mem_cgroup_swapout() clears folio_memcg() */
if (reclaimed && !mapping_exiting(mapping))
shadow = workingset_eviction(folio, target_memcg);
- mem_cgroup_swapout(folio, swap);
__delete_from_swap_cache(folio, swap, shadow);
+ mem_cgroup_swapout(folio, swap);
xa_unlock_irq(&mapping->i_pages);
put_swap_folio(folio, swap);
} else {
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
tmpfs-fix-data-loss-from-failed-fallocate.patch
mm-memcg-fix-swapcached-stat-accounting.patch
