On Thu, Mar 17, 2022 at 04:48:22PM -0700, 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.
in fs/xfs/xfs_file.c:
1391 STATIC int
1392 xfs_file_mmap(
1393 struct file *file,
1394 struct vm_area_struct *vma)
1395 {
1396 struct inode *inode = file_inode(file);
1397 struct xfs_buftarg *target = xfs_inode_buftarg(XFS_I(inode));
1398
1399 /*
1400 * We don't support synchronous mappings for non-DAX files and
1401 * for DAX files if underneath dax_device is not synchronous.
1402 */
1403 if (!daxdev_mapping_supported(vma, target->bt_daxdev))
1404 return -EOPNOTSUPP;
1405
1406 file_accessed(file);
1407 vma->vm_ops = &xfs_file_vm_ops;
1408 if (IS_DAX(inode))
1409 vma->vm_flags |= VM_HUGEPAGE;
Are xfs and other filesystems setting VM_HUGEPAGE flag even if it can
never be collapsed?
1410 return 0;
1411 }
> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
> ---
> mm/khugepaged.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 82c71c6da9ce..a0e4fa33660e 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -448,6 +448,10 @@ 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;
> --
> 2.26.3
>
>
--
Thank you, You are awesome!
Hyeonggon :-)
