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SubjectRe: [PATCH v2] mm/THP: use hugepage_vma_check() in khugepaged_enter_vma_merge()
On Tue, May 22, 2018 at 12:44:30PM -0700, Song Liu wrote:
> khugepaged_enter_vma_merge() is using a different approach to check
> whether a vma is valid for khugepaged_enter():
>
> if (!vma->anon_vma)
> /*
> * Not yet faulted in so we will register later in the
> * page fault if needed.
> */
> return 0;
> if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
> /* khugepaged not yet working on file or special mappings */
> return 0;
>
> This check has some problems. One of the obvious problems is that
> it doesn't check shmem_file(), so that vma backed with shmem files
> will not call khugepaged_enter(). Here is an example of failed madvise():
>
> /* mount /dev/shm with huge=advise:
> * mount -o remount,huge=advise /dev/shm */
> /* create file /dev/shm/huge */
> #define HUGE_FILE "/dev/shm/huge"
>
> fd = open(HUGE_FILE, O_RDONLY);
> ptr = mmap(NULL, FILE_SIZE, PROT_READ, MAP_PRIVATE, fd, 0);
> ret = madvise(ptr, FILE_SIZE, MADV_HUGEPAGE);
>
> madvise() will return 0, but this memory region is never put in huge
> page (check from /proc/meminfo: ShmemHugePages).
>
> This patch fixes these problems by reusing hugepage_vma_check() in
> khugepaged_enter_vma_merge().
>
> vma->vm_flags is not yet updated in khugepaged_enter_vma_merge(),
> so we need to pass the new vm_flags to hugepage_vma_check() through
> a separate argument.
>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> mm/khugepaged.c | 26 ++++++++++++--------------
> 1 file changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index d7b2a4b..9f74e51 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -430,18 +430,15 @@ int __khugepaged_enter(struct mm_struct *mm)
> return 0;
> }
>
> +static bool hugepage_vma_check(struct vm_area_struct *vma,
> + unsigned long vm_flags);
> +

The patch looks good to me.

But can we move hugepage_vma_check() here to avoid forward declaration of
the function?

--
Kirill A. Shutemov

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