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

[Baolin Wang]

On 11/6/26 2:16 AM, 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>
> ---

Make sense to me.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>