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mm: fix incorrect vm_flags usage when checking allowable orders for tmpfs

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Lance reported that when nothing else causes the mm to be considered for
khugepaged collapse, an MADV_HUGEPAGE-advised tmpfs VMA alone does not
trigger scanning.

After commit 6beeab870e ("mm: shmem: move shmem_huge_global_enabled()
into shmem_allowable_huge_orders()"), the shmem/tmpfs allowable order
check reads vma->flags directly.  However, when MADV_HUGEPAGE is handled,
khugepaged_enter_vma() is called before the VMA's flags have been updated,
so the check uses stale flags and incorrectly rejects the VMA for
collapse.  As a result, khugepaged does not collapse the tmpfs file into
PMD order in time.

Fix this by calling khugepaged_enter_vma() with the new VMA flags in
madvise_update_vma().  Meanwhile we can remove the khugepaged_enter_vma()
in hugepage_madvise().

Link: https://lore.kernel.org/7d5b5eb27be798f89d563b06254c947ff53db0b2.1787020910.git.baolin.wang@linux.alibaba.com
Fixes: 6beeab870e ("mm: shmem: move shmem_huge_global_enabled() into shmem_allowable_huge_orders()")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reported-by: Lance Yang <lance.yang@linux.dev>
Closes: https://lore.kernel.org/all/20260815181632.21453-1-lance.yang@linux.dev/
Suggested-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Baolin Wang
2026-08-18 10:47:26 +08:00
committed by Andrew Morton
parent 267bede12d
commit 2fd4e76936
2 changed files with 8 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
mm/khugepaged.c
View File

@@ -454,12 +454,6 @@ int hugepage_madvise(struct vm_area_struct *vma,
case MADV_HUGEPAGE:
*vm_flags &= ~VM_NOHUGEPAGE;
*vm_flags |= VM_HUGEPAGE;
/*
* If the vma become good for khugepaged to scan,
* register it here without waiting a page fault that
* may not happen any time soon.
*/
khugepaged_enter_vma(vma, *vm_flags);
break;
case MADV_NOHUGEPAGE:
*vm_flags &= ~VM_HUGEPAGE;

8
mm/madvise.c
View File

@@ -178,6 +178,14 @@ static int madvise_update_vma(vm_flags_t new_flags,
/* vm_flags is protected by the mmap_lock held in write mode. */
vma_start_write(vma);
vma->flags = new_vma_flags;
/*
* If the vma become good for khugepaged to scan,
* register it here without waiting a page fault that
* may not happen any time soon.
*/
if (vma_flags_test(&new_vma_flags, VMA_HUGEPAGE_BIT))
khugepaged_enter_vma(vma, vma_flags_to_legacy(new_vma_flags));
if (set_new_anon_name)
return replace_anon_vma_name(vma, anon_name);