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SubjectRe: [v3 PATCH 0/2] Fix false negative of shmem vma's THP eligibility
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Hi Hugh,


Any comments for this version? Although they have been in -mm tree, they
didn't make in 5.3 merge window, I'm supposed Andrew needs ack from you
or someone else.


Thanks,

Yang



On 6/12/19 9:43 PM, Yang Shi wrote:
> The commit 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 shmem objects should be treated
> separately from anonymous 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.
>
> The transhuge_vma_suitable() is needed to check vma, but it was only
> available for shmem THP. The patch 1/2 makes it available for all kind of
> THPs and does some code duplication cleanup, so it is made a separate patch.
>
>
> Changelog:
> v3: * Check if vma is suitable for allocating THP per Hugh Dickins
> * Fixed smaps output alignment and documentation per Hugh Dickins
> v2: * Check VM_NOHUGEPAGE per Michal Hocko
>
>
> Yang Shi (2):
> mm: thp: make transhuge_vma_suitable available for anonymous THP
> mm: thp: fix false negative of shmem vma's THP eligibility
>
> Documentation/filesystems/proc.txt | 4 ++--
> fs/proc/task_mmu.c | 3 ++-
> mm/huge_memory.c | 11 ++++++++---
> mm/internal.h | 25 +++++++++++++++++++++++++
> mm/memory.c | 13 -------------
> mm/shmem.c | 3 +++
> 6 files changed, 40 insertions(+), 19 deletions(-)

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