The patch titled
Subject: workingset: fix confusion around eviction vs refault container
has been added to the -mm mm-unstable branch. Its filename is
workingset-fix-confusion-around-eviction-vs-refault-container.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/workingset-fix-confusion-around-eviction-vs-refault-container.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: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: workingset: fix confusion around eviction vs refault container
Date: Wed, 4 Jan 2023 14:29:44 -0800
Refault decisions are made based on the lruvec where the page was evicted,
as that determined its LRU order while it was alive. Stats and workingset
aging must then occur on the lruvec of the new page, as that's the node
and cgroup that experience the refault and that's the lruvec whose
nonresident info ages out by a new resident page. Those lruvecs could be
different when a page is shared between cgroups, or the refaulting page is
allocated on a different node.
There are currently two mix-ups:
1. When swap is available, the resident anon set must be considered
when comparing the refault distance. The comparison is made against
the right anon set, but the check for swap is not. When pages get
evicted from a cgroup with swap, and refault in one without, this
can incorrectly consider a hot refault as cold - and vice
versa. Fix that by using the eviction cgroup for the swap check.
2. The stats and workingset age are updated against the wrong lruvec
altogether: the right cgroup but the wrong NUMA node. When a page
refaults on a different NUMA node, this will have confusing stats
and distort the workingset age on a different lruvec - again
possibly resulting in hot/cold misclassifications down the line.
Fix the swap check and the refault pgdat to address both concerns.
This was found during code review. It hasn't caused notable issues in
production, suggesting that those refault-migrations are relatively rare
in practice.
Link: https://lkml.kernel.org/r/20230104222944.2380117-1-nphamcs@xxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Co-developed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/workingset.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/workingset.c~workingset-fix-confusion-around-eviction-vs-refault-container
+++ a/mm/workingset.c
@@ -457,6 +457,7 @@ void workingset_refault(struct folio *fo
*/
nr = folio_nr_pages(folio);
memcg = folio_memcg(folio);
+ pgdat = folio_pgdat(folio);
lruvec = mem_cgroup_lruvec(memcg, pgdat);
mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
@@ -474,7 +475,7 @@ void workingset_refault(struct folio *fo
workingset_size += lruvec_page_state(eviction_lruvec,
NR_INACTIVE_FILE);
}
- if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
+ if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
workingset_size += lruvec_page_state(eviction_lruvec,
NR_ACTIVE_ANON);
if (file) {
_
Patches currently in -mm which might be from hannes@xxxxxxxxxxx are
mm-memcontrol-skip-moving-non-present-pages-that-are-mapped-elsewhere.patch
mm-rmap-remove-lock_page_memcg.patch
mm-memcontrol-deprecate-charge-moving.patch
workingset-fix-confusion-around-eviction-vs-refault-container.patch
