linux-ext4 - [PATCH 3/8] mm: khugepaged: skip DAX vma

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Date:   Mon, 28 Feb 2022 15:57:36 -0800
From:   Yang Shi <shy828301@...il.com>
To:     vbabka@...e.cz, kirill.shutemov@...ux.intel.com,
        songliubraving@...com, linmiaohe@...wei.com, riel@...riel.com,
        willy@...radead.org, ziy@...dia.com, akpm@...ux-foundation.org,
        tytso@....edu, adilger.kernel@...ger.ca, darrick.wong@...cle.com
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/8] mm: khugepaged: skip DAX vma

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.

Signed-off-by: Yang Shi <shy828301@...il.com>
---
 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