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

[Baolin Wang]

On 9/11/26 7:37 PM, Kiryl Shutsemau wrote:
> 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")

Ah. You are right. Will update in v2.

> > 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>

Thanks.