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

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Message-ID: <9b7afb6a-b709-4b42-a4dc-fa12c2ca624c@kernel.org>
Date: Mon, 9 Feb 2026 16:31:13 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 catalin.marinas@....com, will@...nel.org
Cc: lorenzo.stoakes@...cle.com, ryan.roberts@....com,
 Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com,
 mhocko@...e.com, riel@...riel.com, harry.yoo@...cle.com, jannh@...gle.com,
 willy@...radead.org, baohua@...nel.org, dev.jain@....com,
 linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/5] mm: rmap: support batched unmapping for file large
 folios

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@....com>
> Acked-by: Barry Song <baohua@...nel.org>
> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

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

-- 
Cheers,

David