From 66ee95d16a7f1b7b4f1dd74a2d81c6e19dc29a14 Mon Sep 17 00:00:00 2001 From: Steve Capper Date: Thu, 28 Apr 2016 16:18:24 -0700 Subject: [PATCH] mm: exclude HugeTLB pages from THP page_mapped() logic HugeTLB pages cannot be split, so we use the compound_mapcount to track rmaps. Currently page_mapped() will check the compound_mapcount, but will also go through the constituent pages of a THP compound page and query the individual _mapcount's too. Unfortunately, page_mapped() does not distinguish between HugeTLB and THP compound pages and assumes that a compound page always needs to have HPAGE_PMD_NR pages querying. For most cases when dealing with HugeTLB this is just inefficient, but for scenarios where the HugeTLB page size is less than the pmd block size (e.g. when using contiguous bit on ARM) this can lead to crashes. This patch adjusts the page_mapped function such that we skip the unnecessary THP reference checks for HugeTLB pages. Fixes: e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() for compound pages") Signed-off-by: Steve Capper Acked-by: Kirill A. Shutemov Cc: Will Deacon Cc: Catalin Marinas Cc: Michal Hocko Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index a55e5be0894f..79b6c18d0a38 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1031,6 +1031,8 @@ static inline bool page_mapped(struct page *page) page = compound_head(page); if (atomic_read(compound_mapcount_ptr(page)) >= 0) return true; + if (PageHuge(page)) + return false; for (i = 0; i < hpage_nr_pages(page); i++) { if (atomic_read(&page[i]._mapcount) >= 0) return true; -- 2.20.1