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

[Lance Yang]

On Thu, Nov 05, 2026 at 07:16:44PM +0100, 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>
>---

Nice work1

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>