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SubjectRe: [v3 PATCH 3/8] mm: khugepaged: skip DAX vma
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On 4/4/22 22:02, Yang Shi wrote:
> The DAX vma may be seen by khugepaged when the mm has other khugepaged
> suitable vmas. So khugepaged may try to collapse THP for DAX vma, but
> it will fail due to page sanity check, for example, page is not
> on LRU.
>
> So it is not harmful, but it is definitely pointless to run khugepaged
> against DAX vma, so skip it in early check.
>
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> Acked-by: Song Liu <song@kernel.org>
> Signed-off-by: Yang Shi <shy828301@gmail.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/khugepaged.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 7d197d9e3258..964a4d2c942a 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -447,6 +447,10 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
> if (vm_flags & VM_NO_KHUGEPAGED)
> return false;
>
> + /* Don't run khugepaged against DAX vma */
> + if (vma_is_dax(vma))
> + return false;
> +
> if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> vma->vm_pgoff, HPAGE_PMD_NR))
> return false;

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