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

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Message-ID: <CAMgjq7Bqffjm3dTZ+bHALisCkw7ASao_1h4ZZVM6kd14YdKzmA@mail.gmail.com>
Date: Wed, 3 Sep 2025 01:13:57 +0800
From: Kairui Song <ryncsn@...il.com>
To: David Hildenbrand <david@...hat.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 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...

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

> --
> Cheers
>
> David / dhildenb
>
>