The patch titled
Subject: vmscan,migrate: fix page count imbalance on node stats when demoting pages
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
vmscanmigrate-fix-double-decrement-on-node-stats-when-demoting-pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/vmscanmigrate-fix-double-decrement-on-node-stats-when-demoting-pages.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Gregory Price <gourry@xxxxxxxxxx>
Subject: vmscan,migrate: fix page count imbalance on node stats when demoting pages
Date: Fri, 25 Oct 2024 10:17:24 -0400
When numa balancing is enabled with demotion, vmscan will call
migrate_pages when shrinking LRUs. migrate_pages will decrement the
the node's isolated page count, leading to an imbalanced count when
invoked from (MG)LRU code.
The result is dmesg output like such:
$ cat /proc/sys/vm/stat_refresh
[77383.088417] vmstat_refresh: nr_isolated_anon -103212
[77383.088417] vmstat_refresh: nr_isolated_file -899642
This negative value may impact compaction and reclaim throttling.
The following path produces the decrement:
shrink_folio_list
demote_folio_list
migrate_pages
migrate_pages_batch
migrate_folio_move
migrate_folio_done
mod_node_page_state(-ve) <- decrement
This path happens for SUCCESSFUL migrations, not failures. Typically
callers to migrate_pages are required to handle putback/accounting for
failures, but this is already handled in the shrink code.
When accounting for migrations, instead do not decrement the count when
the migration reason is MR_DEMOTION. As of v6.11, this demotion logic
is the only source of MR_DEMOTION.
Link: https://lkml.kernel.org/r/20241025141724.17927-1-gourry@xxxxxxxxxx
Fixes: 26aa2d199d6f ("mm/migrate: demote pages during reclaim")
Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/migrate.c~vmscanmigrate-fix-double-decrement-on-node-stats-when-demoting-pages
+++ a/mm/migrate.c
@@ -1178,7 +1178,7 @@ static void migrate_folio_done(struct fo
* not accounted to NR_ISOLATED_*. They can be recognized
* as __folio_test_movable
*/
- if (likely(!__folio_test_movable(src)))
+ if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
folio_is_file_lru(src), -folio_nr_pages(src));
_
Patches currently in -mm which might be from gourry@xxxxxxxxxx are
vmscanmigrate-fix-double-decrement-on-node-stats-when-demoting-pages.patch
