The patch titled
Subject: mm/shmem.c: fix judgment error in shmem_is_huge()
has been added to the -mm tree. Its filename is
fix-judgment-error-in-shmem_is_huge.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/fix-judgment-error-in-shmem_is_huge.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/fix-judgment-error-in-shmem_is_huge.patch
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------------------------------------------------------
From: Liu Yuntao <liuyuntao10@xxxxxxxxxx>
Subject: mm/shmem.c: fix judgment error in shmem_is_huge()
In the case of SHMEM_HUGE_WITHIN_SIZE, the page index is not rounded up
correctly. When the page index points to the first page in a huge page,
round_up() cannot bring it to the end of the huge page, but to the end of
the previous one.
An example:
HPAGE_PMD_NR on my machine is 512(2 MB huge page size). After allcoating
a 3000 KB buffer, I access it at location 2050 KB. In shmem_is_huge(),
the corresponding index happens to be 512. After rounded up by
HPAGE_PMD_NR, it will still be 512 which is smaller than i_size, and
shmem_is_huge() will return true. As a result, my buffer takes an
additional huge page, and that shouldn't happen when shmem_enabled is set
to within_size.
Link: https://lkml.kernel.org/r/20210909032007.18353-1-liuyuntao10@xxxxxxxxxx
Fixes: f3f0e1d2150b2b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Liu Yuntao <liuyuntao10@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: wuxu.wu <wuxu.wu@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/shmem.c~fix-judgment-error-in-shmem_is_huge
+++ a/mm/shmem.c
@@ -490,9 +490,9 @@ bool shmem_is_huge(struct vm_area_struct
case SHMEM_HUGE_ALWAYS:
return true;
case SHMEM_HUGE_WITHIN_SIZE:
- index = round_up(index, HPAGE_PMD_NR);
+ index = round_up(index + 1, HPAGE_PMD_NR);
i_size = round_up(i_size_read(inode), PAGE_SIZE);
- if (i_size >= HPAGE_PMD_SIZE && (i_size >> PAGE_SHIFT) >= index)
+ if (i_size >> PAGE_SHIFT >= index)
return true;
fallthrough;
case SHMEM_HUGE_ADVISE:
_
Patches currently in -mm which might be from liuyuntao10@xxxxxxxxxx are
fix-judgment-error-in-shmem_is_huge.patch
