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SubjectRe: [v2 PATCH 1/2] mm: thp: register mm for khugepaged when merging vma for shmem
On Thu, Jun 21, 2018 at 11:15:48PM +0000, yang.shi@linux.alibaba.com wrote:
> When merging anonymous page vma, if the size of vma can fit in at least
> one hugepage, the mm will be registered for khugepaged for collapsing
> THP in the future.
>
> But, it skips shmem vma. Doing so for shmem too, but not file-private
> mapping, when merging vma in order to increase the odd to collapse
> hugepage by khugepaged.
>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
> v1 --> 2:
> * Exclude file-private mapping per Kirill's comment
>
> mm/khugepaged.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index d7b2a4b..9b0ec30 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -440,8 +440,12 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
> * page fault if needed.
> */
> return 0;
> - if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
> - /* khugepaged not yet working on file or special mappings */
> + if ((vma->vm_ops && (!shmem_file(vma->vm_file) || vma->anon_vma)) ||
> + (vm_flags & VM_NO_KHUGEPAGED))
> + /*
> + * khugepaged not yet working on non-shmem file or special
> + * mappings. And, file-private shmem THP is not supported.
> + */
> return 0;

My point was that vma->anon_vma check above this one should not prevent
collapse for shmem.

Looking into this more, I think we should just replace all these checks
with hugepage_vma_check() call.

--
Kirill A. Shutemov

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