Re: [PATCH v6 5/5] mm: rmap: support batched unmapping for file large folios

David Hildenbrand (Arm)
2026-02-09T15:31:26Z

On 2/9/26 15:07, Baolin Wang wrote:
> Similar to folio_referenced_one(), we can apply batched unmapping for file
> large folios to optimize the performance of file folios reclamation.
>
> Barry previously implemented batched unmapping for lazyfree anonymous large
> folios[1] and did not further optimize anonymous large folios or file-backed
> large folios at that stage. As for file-backed large folios, the batched
> unmapping support is relatively straightforward, as we only need to clear
> the consecutive (present) PTE entries for file-backed large folios.
>
> Note that it's not ready to support batched unmapping for uffd case, so
> let's still fallback to per-page unmapping for the uffd case.
>
> Performance testing:
> Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and try to
> reclaim 8G file-backed folios via the memory.reclaim interface. I can observe
> 75% performance improvement on my Arm64 32-core server (and 50%+ improvement
> on my X86 machine) with this patch.
>
> W/o patch:
> real 0m1.018s
> user 0m0.000s
> sys 0m1.018s
>
> W/ patch:
> real 0m0.249s
> user 0m0.000s
> sys 0m0.249s
>
> [1] https://lore.kernel.org/all/20250214093015.51024-4-21cnbao@gmail.com/T/#u
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> Acked-by: Barry Song <baohua@kernel.org>
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

--
Cheers,

David