From 10d483f198cf35504fcffc677ac116190839a34f Mon Sep 17 00:00:00 2001 From: Baolin Wang Date: Wed, 9 Apr 2025 17:38:58 +0800 Subject: [PATCH] mm: huge_memory: add folio_mark_accessed() when zapping file THP When investigating performance issues during file folio unmap, I noticed some behavioral differences in handling non-PMD-sized folios and PMD-sized folios. For non-PMD-sized file folios, it will call folio_mark_accessed() to mark the folio as having seen activity, but this is not done for PMD-sized folios. This might not cause obvious issues, but a potential problem could be that, it might lead to reclaim of hot file folios under memory pressure, as quoted from Johannes: : Sometimes file contents are only accessed through relatively short-lived : mappings. But they can nevertheless be accessed a lot and be hot. It's : important to not lose that information on unmap, and end up kicking out a : frequently used cache page. Therefore, we should also add folio_mark_accessed() for PMD-sized file folios when unmapping. [baolin.wang@linux.alibaba.com: add comment] Link: https://lkml.kernel.org/r/23fdc11d-e983-4627-89a8-79e9ecf9a45a@linux.alibaba.com Link: https://lkml.kernel.org/r/fc117f60d7b686f87067f36a0ef7cdbc3a78109c.1744190345.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Acked-by: Johannes Weiner Acked-by: Zi Yan Acked-by: David Hildenbrand Reviewed-by: Oscar Salvador Cc: Barry Song <21cnbao@gmail.com> Cc: Matthew Wilcox (Oracle) Cc: Ryan Roberts Signed-off-by: Andrew Morton --- mm/huge_memory.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1cd975503131a..5576a08a593dc 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2259,6 +2259,14 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, zap_deposited_table(tlb->mm, pmd); add_mm_counter(tlb->mm, mm_counter_file(folio), -HPAGE_PMD_NR); + + /* + * Use flush_needed to indicate whether the PMD entry + * is present, instead of checking pmd_present() again. + */ + if (flush_needed && pmd_young(orig_pmd) && + likely(vma_has_recency(vma))) + folio_mark_accessed(folio); } spin_unlock(ptl); -- 2.47.2