Re: [PATCH v2 09/14] mm/shmem: rescan after nonuniform folio splitting

["Zi Yan" <ziy@nvidia.com>]

On Tue Oct 27, 2026 at 9:03 AM EDT, David Hildenbrand (Arm) wrote:
> The final scan in shmem_undo_range() restarts after a successful split
> only if the original folio is no longer large. A nonuniform split can
> leave that folio large, so the scan skips the newly created folios.
> Hole punching then leaves pages within the hole allocated even though
> they could be discarded.
>
> For example, a fault below the hole can allocate a 2 MiB folio after
> boundary handling. Punching a 1 MiB hole at offset 64 KiB splits the
> folio successfully but leaves the original folio at order 4. The scan
> continues past all 512 pages, leaving 2 MiB allocated instead of 1 MiB.
> The hole reads as zero, but the pages and their block charges remain.
>
> Fixes: 7460b470a131 ("mm/truncate: use folio_split() in truncate operation")
> Cc: stable@vger.kernel.org
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> Tested-by: Gregory Price (Meta) <gourry@gourry.net>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
> ---
>  mm/shmem.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
>
Reviewed-by: Zi Yan <ziy@nvidia.com>

-- 
Best Regards,
Yan, Zi