Re: [PATCH v2] mm: shmem: ignore sysfs configs for shmem forced collapse

[Barry Song]

On Mon, Sep 14, 2026 at 10:13 AM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>
> 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.
>
> 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: 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/
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> Acked-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---

LGTM,

Reviewed-by: Barry Song <baohua@xxxxxxxxxx>