linux-kernel - Re: [PATCH v2 02/15] mm, swap: use unified helper for swap cache look up

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Message-ID: <ca6c572f-e63d-4de9-895f-2da4a2658c46@redhat.com>
Date: Mon, 8 Sep 2025 13:43:59 +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 v2 02/15] mm, swap: use unified helper for swap cache look
 up

On 05.09.25 21:13, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> The swap cache lookup helper swap_cache_get_folio currently does
> readahead updates as well, so callers that are not doing swapin from any
> VMA or mapping are forced to reuse filemap helpers instead, and have to
> access the swap cache space directly.
> 
> So decouple readahead update with swap cache lookup. Move the readahead
> update part into a standalone helper. Let the caller call the readahead
> update helper if they do readahead. 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. The following commits will wrap
> their accesses to the swap cache too, with special helpers.
> 
> And worth noting, currently dropbehind is not supported for anon folio,
> and we will never see a dropbehind folio in swap cache. The unified
> helper can be updated later to handle that.
> 
> While at it, add proper kernedoc for touched helpers.
> 
> No functional change.
> 
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Acked-by: Chris Li <chrisl@...nel.org>
> Acked-by: Nhat Pham <nphamcs@...il.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Reviewed-by: Barry Song <baohua@...nel.org>
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb