linux-kernel - Re: [PATCH v5 0/5] support batch checking of references and unmapping for large folios

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Message-ID: <3595c849-6b43-440e-8e15-f51d5de0cad6@kernel.org>
Date: Fri, 16 Jan 2026 11:52:22 +0100
From: "David Hildenbrand (Red Hat)" <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 v5 0/5] support batch checking of references and unmapping
 for large folios

On 12/26/25 07:07, Baolin Wang wrote:
> Currently, folio_referenced_one() always checks the young flag for each PTE
> sequentially, which is inefficient for large folios. This inefficiency is
> especially noticeable when reclaiming clean file-backed large folios, where
> folio_referenced() is observed as a significant performance hotspot.
> 
> Moreover, on Arm architecture, which supports contiguous PTEs, there is already
> an optimization to clear the young flags for PTEs within a contiguous range.
> However, this is not sufficient. We can extend this to perform batched operations
> for the entire large folio (which might exceed the contiguous range: CONT_PTE_SIZE).
> 
> Similar to folio_referenced_one(), we can also apply batched unmapping for large
> file folios to optimize the performance of file folio reclamation. By supporting
> batched checking of the young flags, flushing TLB entries, and unmapping, I can
> observed a significant performance improvements in my performance tests for file
> folios reclamation. Please check the performance data in the commit message of
> each patch.
> 
> Run stress-ng and mm selftests, no issues were found.


Baolin, I'm intending to review this, but it might still take me a bit 
until I get to it. (PTO/vacation and other fun)

-- 
Cheers

David