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mm: khugepaged: better comments for anon vma check in hugepage_vma_revalidate

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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.

Link: https://lkml.kernel.org/r/20220616174840.1202070-4-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zach O'Keefe <zokeefe@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yang Shi 2022-06-16 10:48:36 -07:00 committed by akpm
parent 4fa6893fae
commit f707fa4937
1 changed files with 7 additions and 1 deletions
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8
mm/khugepaged.c
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@ -958,7 +958,13 @@ 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;