linux-kernel - Re: [PATCH 1/9] mm, swap: use unified helper for swap cache look up

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Message-ID: <e22b8472-6d20-49b4-b49b-78f79f126294@redhat.com>
Date: Tue, 2 Sep 2025 12:10:08 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>,
 Chris Li <chrisl@...nel.org>, Barry Song <baohua@...nel.org>,
 Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
 Kemeng Shi <shikemeng@...weicloud.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosryahmed@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] mm, swap: use unified helper for swap cache look up

On 22.08.25 21:20, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> Always use swap_cache_get_folio for swap cache folio look up. The reason
> we are not using it in all places is that it also updates the readahead
> info, and some callsites want to avoid that.
> 
> So decouple readahead update with swap cache lookup into a standalone
> helper, let the caller call the readahead update helper if that's
> needed. And convert all swap cache lookups to use swap_cache_get_folio.
> 
> After this commit, there are only three special cases for accessing swap
> cache space now: huge memory splitting, migration and shmem replacing,
> because they need to lock the Xarray. Following commits will wrap their
> accesses to the swap cache too with special helpers.
> 
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---



> +void swap_update_readahead(struct folio *folio,
> +			   struct vm_area_struct *vma,
> +			   unsigned long addr)
>   {

Oh, one thing. Regarding recent const-correctness discussions, "folio" 
should probably be const here.

-- 
Cheers

David / dhildenb