From 72c3d682c165b836b54a3d07a01f72e39c47022c Mon Sep 17 00:00:00 2001 From: Baolin Wang Date: Mon, 14 Sep 2026 10:12:41 +0800 Subject: [PATCH] mm: shmem: ignore sysfs configs for shmem forced collapse According to Documentation/mm/transhuge.rst, MADV_COLLAPSE is expected to ignore any THP or mTHP interface settings. However, after commit 26c7d8413aaf ("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: 26c7d8413aaf ("mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem") Signed-off-by: Baolin Wang Signed-off-by: Andrew Morton Reported-by: Kiryl Shutsemau (Meta) Closes: https://lore.kernel.org/all/20260908125105.1510704-7-kirill@shutemov.name/ Reviewed-by: Kiryl Shutsemau (Meta) Acked-by: Zi Yan Reviewed-by: Lance Yang Reviewed-by: Barry Song Acked-by: Qi Zheng Acked-by: David Hildenbrand (Arm) Reviewed-by: Lorenzo Stoakes (ARM) Cc: Dev Jain Cc: Hugh Dickins Cc: Liam R. Howlett Cc: Ryan Roberts Cc: --- mm/shmem.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 897fa2b61346..848316eaa7f4 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1847,8 +1847,11 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode, global_orders = shmem_huge_global_enabled(inode, index, write_end, shmem_huge_force, vma, vm_flags); - /* Tmpfs huge pages allocation */ - if (!vma || !vma_is_anon_shmem(vma)) + /* + * Tmpfs huge pages allocation or forced collapse ignores + * sysfs configs. + */ + if (!vma || !vma_is_anon_shmem(vma) || shmem_huge_force) return global_orders; /*