Re: [PATCH] mm: shmem: ignore sysfs configs for shmem forced collapse

[Kiryl Shutsemau]

On Fri, Sep 11, 2026 at 12:04:33PM +0800, Baolin Wang wrote:
> According to Documentation/mm/transhuge.rst, MADV_COLLAPSE is expected to
> ignore any THP or mTHP interface settings.
> 
> However, after commit 6beeab870e70 ("mm: shmem: move shmem_huge_global_enabled()
> into shmem_allowable_huge_orders()"), 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.
> 
> 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.
> 
> Fixes: 6beeab870e70 ("mm: shmem: move shmem_huge_global_enabled() into shmem_allowable_huge_orders()")

Hm. I don't think it is the right Fixes tag. "No functional changes" in
its commit message seems to be true.

This might be a better fit:

Fixes: 26c7d8413aaf ("mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem")

> Reported-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20260908125105.1510704-7-kirill@xxxxxxxxxxxxx/
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

Thanks!

Reviewed-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>


-- 
  Kiryl Shutsemau / Kirill A. Shutemov