On 7/24/25 00:31, Konstantin Khorenko wrote:
The function was checking cache flag on the new folio instead of the old one,
causing cache counter imbalance when replacing cache pages.
The new folio is freshly allocated and never has the cache flag set, so
we need to copy the flag from the old folio and charge the cache counter
accordingly.
This fixes potential cache accounting issues during page cache replacement
operations like page migration between NUMA nodes.
Fixes: 763a087e29d11 ("mm: Memory cgroup page cache limit")
https://virtuozzo.atlassian.net/browse/VSTOR-111756
Signed-off-by: Konstantin Khorenko <khore...@virtuozzo.com>
Feature: mm: Memory cgroup page cache limit
---
mm/memcontrol.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cefb72234fda5..af70959f00c8e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -8292,6 +8292,12 @@ void mem_cgroup_migrate(struct folio *old, struct folio
*new)
page_counter_charge(&memcg->memsw, nr_pages);
}
+ if (folio_memcg_cache(old)) {
+ WRITE_ONCE(folio->memcg_data,
We don't seem to have "folio" variable here on vz9 (at least I checked
in rh9-5.14.0-427.77.1.vz9.86.2), probably meant to be "new".
+ READ_ONCE(folio->memcg_data) | MEMCG_DATA_PGCACHE);
+ page_counter_charge(&memcg->cache, nr_pages);
+ }
+
/*
* finist explained the idea behind adding a WARN_ON() here:
* - we do not want to check flags correctness on each flag change
@@ -8312,9 +8318,6 @@ void mem_cgroup_migrate(struct folio *old, struct folio
*new)
folio_test_swapbacked(new) || folio_test_swapcache(new) ||
folio_test_mappedtodisk(new) || folio_test_ksm(new)));
- if (folio_memcg_cache(new))
- page_counter_charge(&memcg->cache, nr_pages);
-
css_get(&memcg->css);
commit_charge(new, memcg);
This commit_charge is probably making all our efforts vain, as it resets
flags in new->memcg_data by putting memory cgroup pointer there. E.g. in
charge_memcg we first do commit_charge and only then add our flag to it.
I believe we must put WRITE_ONCE after commit_charge, same for our
"WARN_ON(folio_memcg_cache(new)...".
--
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.
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