The patch titled
Subject: mm: thp: fix false negative of shmem vma's THP eligibility
has been added to the -mm tree. Its filename is
mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility.patch
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------------------------------------------------------
From: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Subject: mm: thp: fix false negative of shmem vma's THP eligibility
7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma")
introduced THPeligible bit for processes' smaps. But, when checking the
eligibility for shmem vma, __transparent_hugepage_enabled() is called to
override the result from shmem_huge_enabled(). It may result in the
anonymous vma's THP flag override shmem's. For example, running a simple
test which create THP for shmem, but with anonymous THP disabled, when
reading the process's smaps, it may show:
7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test
Size: 4096 kB
...
[snip]
...
ShmemPmdMapped: 4096 kB
...
[snip]
...
THPeligible: 0
And, /proc/meminfo does show THP allocated and PMD mapped too:
ShmemHugePages: 4096 kB
ShmemPmdMapped: 4096 kB
This doesn't make too much sense. The anonymous THP flag should not
intervene shmem THP. Calling shmem_huge_enabled() with checking
MMF_DISABLE_THP sounds good enough. And, we could skip stack and dax vma
check since we already checked if the vma is shmem already.
Link: http://lkml.kernel.org/r/1555971893-52276-1-git-send-email-yang.shi@xxxxxxxxxxxxxxxxx
Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma")
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 4 ++--
mm/shmem.c | 2 ++
2 files changed, 4 insertions(+), 2 deletions(-)
--- a/mm/huge_memory.c~mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility
+++ a/mm/huge_memory.c
@@ -67,8 +67,8 @@ bool transparent_hugepage_enabled(struct
{
if (vma_is_anonymous(vma))
return __transparent_hugepage_enabled(vma);
- if (vma_is_shmem(vma) && shmem_huge_enabled(vma))
- return __transparent_hugepage_enabled(vma);
+ if (vma_is_shmem(vma))
+ return shmem_huge_enabled(vma);
return false;
}
--- a/mm/shmem.c~mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility
+++ a/mm/shmem.c
@@ -3873,6 +3873,8 @@ bool shmem_huge_enabled(struct vm_area_s
loff_t i_size;
pgoff_t off;
+ if (test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
+ return false;
if (shmem_huge == SHMEM_HUGE_FORCE)
return true;
if (shmem_huge == SHMEM_HUGE_DENY)
_
Patches currently in -mm which might be from yang.shi@xxxxxxxxxxxxxxxxx are
mm-thp-fix-false-negative-of-shmem-vmas-thp-eligibility.patch
doc-mm-migration-doesnt-use-foll_split-anymore.patch
