linux-kernel - [v4 PATCH 3/7] mm: khugepaged: better comments for anon vma check in hugepage_vma

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Message-Id: <20220615172926.546974-4-shy828301@gmail.com>
Date:   Wed, 15 Jun 2022 10:29:22 -0700
From:   Yang Shi <shy828301@...il.com>
To:     vbabka@...e.cz, kirill.shutemov@...ux.intel.com,
        willy@...radead.org, zokeefe@...gle.com, linmiaohe@...wei.com,
        akpm@...ux-foundation.org
Cc:     shy828301@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [v4 PATCH 3/7] mm: khugepaged: better comments for anon vma check in hugepage_vma_revalidate

The hugepage_vma_revalidate() needs to check if the vma is still
anonymous vma or not since the address may be unmapped then remapped to
file before khugepaged reaquired the mmap_lock.

The old comment is not quite helpful, elaborate this with better
comment.

Signed-off-by: Yang Shi <shy828301@...il.com>
---
 mm/khugepaged.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index db0b334a7d1f..5baa394e34c8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -960,7 +960,13 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
 		return SCAN_ADDRESS_RANGE;
 	if (!hugepage_vma_check(vma, vma->vm_flags))
 		return SCAN_VMA_CHECK;
-	/* Anon VMA expected */
+	/*
+	 * Anon VMA expected, the address may be unmapped then
+	 * remapped to file after khugepaged reaquired the mmap_lock.
+	 *
+	 * hugepage_vma_check may return true for qualified file
+	 * vmas.
+	 */
 	if (!vma->anon_vma || !vma_is_anonymous(vma))
 		return SCAN_VMA_CHECK;
 	return 0;
-- 
2.26.3