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

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Message-ID: <734e09b6-9100-449f-aa77-75a18b634db2@redhat.com>
Date: Wed, 3 Sep 2025 10:00:21 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <ryncsn@...il.com>
Cc: linux-mm@...ck.org, 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 02.09.25 19:13, Kairui Song wrote:
> On Tue, Sep 2, 2025 at 6:13 PM David Hildenbrand <david@...hat.com> wrote:
>>
>> 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.
>>
> 
> Not here, swap_update_readahead does folio_test_clear_readahead so...
> 

Ah, makes sense!

> I'll try add const to other places where I see the folio is const,
> thanks for the info!


Thanks!


-- 
Cheers

David / dhildenb