The patch titled
Subject: mm: exclude HugeTLB pages from THP page_mapped() logic
has been added to the -mm tree. Its filename is
mm-exclude-hugetlb-pages-from-thp-page_mapped-logic.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-exclude-hugetlb-pages-from-thp-page_mapped-logic.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-exclude-hugetlb-pages-from-thp-page_mapped-logic.patch
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From: Steve Capper <steve.capper@xxxxxxx>
Subject: 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 <steve.capper@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.4+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 2 ++
1 file changed, 2 insertions(+)
diff -puN include/linux/mm.h~mm-exclude-hugetlb-pages-from-thp-page_mapped-logic include/linux/mm.h
--- a/include/linux/mm.h~mm-exclude-hugetlb-pages-from-thp-page_mapped-logic
+++ a/include/linux/mm.h
@@ -1031,6 +1031,8 @@ static inline bool page_mapped(struct pa
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;
_
Patches currently in -mm which might be from steve.capper@xxxxxxx are
mm-exclude-hugetlb-pages-from-thp-page_mapped-logic.patch
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