From 35e41024c4c2b02ef8207f61b9004f6956cf037b Mon Sep 17 00:00:00 2001 From: Gregory Price Date: Fri, 25 Oct 2024 10:17:24 -0400 Subject: [PATCH] vmscan,migrate: fix page count imbalance on node stats when demoting pages 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@gourry.net Fixes: 26aa2d199d6f ("mm/migrate: demote pages during reclaim") Signed-off-by: Gregory Price Reviewed-by: Yang Shi Reviewed-by: Davidlohr Bueso Reviewed-by: Shakeel Butt Reviewed-by: "Huang, Ying" Reviewed-by: Oscar Salvador Cc: Dave Hansen Cc: Wei Xu Cc: Signed-off-by: Andrew Morton --- mm/migrate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/migrate.c b/mm/migrate.c index 7e520562d421a..fab84a7760889 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1178,7 +1178,7 @@ static void migrate_folio_done(struct folio *src, * 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));