Re: [PATCH 3/5] mm/mmu_gather: flush pending references early before the folio limit

[Lance Yang]

On Thu, Nov 05, 2026 at 02:10:12PM +0100, David Hildenbrand (Arm) wrote:
>When a task zaps mappings (e.g., MADV_DONTNEED), it can drop the PT lock
>and defer dropping the folio references. In the meantime, page faults
>can refault pagecache folios, creating more references for the same
>folios.
>
>Let's just request a flush after enqueueing a pagecache folio whose
>refcount reached a certain threshold. Start flushing well before new
>references are refused, regardless of the caller's privileges.
>
>This is a temporary measure until we have something better.
>
>Reported-by: Chris Mason <mason@xxxxxxxxxx>
>Fixes: 10ebac4f95e7 ("mm/memory: optimize unmap/zap with PTE-mapped THP")
>Cc: stable@xxxxxxxxxxxxxxx
>Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>---

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