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mm: shmem: ignore sysfs configs for shmem forced collapse

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According to Documentation/mm/transhuge.rst, MADV_COLLAPSE is expected to
ignore any THP or mTHP interface settings.

However, after commit 26c7d8413a ("mm: thp: support "THPeligible"
semantics for mTHP with anonymous shmem"), performing MADV_COLLAPSE on
shmem will depend on /sys/.../hugepages-2048kB/shmem_enabled being set to
"inherit" (although that is the default), which can cause MADV_COLLAPSE to
fail unexpectedly.

This could cause a userspace-visible performance regression.

Fix this by returning the result of shmem_huge_global_enabled() directly
when MADV_COLLAPSE is requested, allowing PMD-order collapse while
ignoring shmem THP/mTHP settings.

Link: https://lore.kernel.org/063f655b4d6c4234f3aa27ed6ecab10283ecb880.1789351825.git.baolin.wang@linux.alibaba.com
Fixes: 26c7d8413a ("mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Closes: https://lore.kernel.org/all/20260908125105.1510704-7-kirill@shutemov.name/
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Baolin Wang 2026-09-14 10:12:41 +08:00 • committed by Andrew Morton
commit 72c3d682c1
1 changed files with 5 additions and 2 deletions
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