Re: [PATCH 10/16] mm/shmem: discard whole new large folios on fallocate rollback

[Kiryl Shutsemau]

On Mon, Oct 26, 2026 at 10:40:43AM +0100, David Hildenbrand (Arm) wrote:
> When undoing a failed fallocate(), shmem_undo_range() must discard each
> newly allocated folio. Its second scan instead passes large
> folios to truncate_inode_partial_folio(), which does not necessarily
> discard the entire large folio, but instead tries splitting it to
> discard only the requested range.
> 
> For example, with huge=always, a failed allocation starting at offset
> 4 KiB can leave page 0 allocated in an otherwise empty file.
> 
> Discard the whole folio when unfalloc is set. Note that we enter this
> path only for folios that are not uptodate, and can consequently be
> dropped without losing any data.
> 
> Fixes: 55ac8bbe358b ("mm/shmem: fix race in shmem_undo_range w/THP")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Acked-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov