Re: [PATCH] mm/khugepaged: don't map folios that are not uptodate in MADV_COLLAPSE

[Zi Yan]

On Thu Nov 5, 2026 at 1:16 PM EST, David Hildenbrand (Arm) wrote:
> madvise(MADV_COLLAPSE) can map PMD-sized pagecache folios that are not
> uptodate. For example, shmem fallocate() can put such folios into the
> page cache.
>
> collapse_file() already refuses to proceed with folios that are not
> uptodate. Let's just do the same in try_collapse_pte_mapped_thp() and skip
> such folios, leaving handling to the page faults.
>
> Note that collapse_file() effectively clears shmem folios through
> shmem_get_folio(); let's keep this fix simple and simply let the page
> fault path deal with that.
>
> Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
> Reported-by: Chris Mason <mason@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> ---
> Once reviewed, I will pick this up in a timely manner.
> ---
>  mm/khugepaged.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
Makes sense.

Acked-by: Zi Yan <ziy@xxxxxxxxxx>

-- 
Best Regards,
Yan, Zi