From 103142868af5a61bc0399ebe71a4dca50d48ff43 Mon Sep 17 00:00:00 2001 From: Usama Arif Date: Wed, 16 Sep 2026 05:51:22 -0700 Subject: [PATCH] mm: filemap: move lruvec accounting outside the xarray lock __filemap_add_folio() inserts a folio and updates mapping->nrpages while holding mapping->i_pages.xa_lock with interrupts disabled. The XArray insertion and nrpages update require the lock, but the lruvec statistic updates do not. With CONFIG_MEMCG, those calls also update per-CPU memcg and lruvec counters and notify cgroup rstat, extending the critical section. Move the lruvec accounting after a successful XArray insertion and after xas_unlock_irq(). The page-cache references pin the folio, while the folio lock keeps folio->mapping stable and prevents removal until accounting is complete. This moves one lruvec update for ordinary folios and a second for PMD-mappable folios out of the serialized section. In a 30-second system-wide perf lock contention -ab capture on a production host, the hottest caller-stack record attributed to __filemap_add_folio() had 20,867 contentions and 557.930 ms total wait. That was 14% of the 3.998 seconds of aggregate lock wait in the capture. Moving lruvec accuting outside of critical section should help optimize it. Link: https://lore.kernel.org/20260916125122.2696271-1-usama.arif@linux.dev Signed-off-by: Usama Arif Signed-off-by: Andrew Morton Reviewed-by: Shakeel Butt Acked-by: Muchun Song Reviewed-by: Vishal Moola (Fractile) Reviewed-by: Jan Kara Cc: David Hildenbrand Cc: Johannes Weiner Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Rik van Riel Cc: Roman Gushchin --- mm/filemap.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 00fd89cf6f55..4720bbfc1a66 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -918,14 +918,6 @@ noinline int __filemap_add_folio(struct address_space *mapping, mapping->nrpages += nr; - /* hugetlb pages do not participate in page cache accounting */ - if (!huge) { - lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr); - if (folio_test_pmd_mappable(folio)) - lruvec_stat_mod_folio(folio, - NR_FILE_THPS, nr); - } - unlock: xas_unlock_irq(&xas); @@ -942,6 +934,13 @@ noinline int __filemap_add_folio(struct address_space *mapping, if (xas_error(&xas)) goto error; + /* hugetlb pages do not participate in page cache accounting */ + if (!huge) { + lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr); + if (folio_test_pmd_mappable(folio)) + lruvec_stat_mod_folio(folio, NR_FILE_THPS, nr); + } + trace_mm_filemap_add_to_page_cache(folio); return 0; error: