linux-kernel - Re: [PATCH 2/2] mm, swap: prefer nonfull over free clusters

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Message-ID: <CAF8kJuObbE+X3WKiO_Nviya129jeAuSXv7tCJ=4tb9SLf1pD7g@mail.gmail.com>
Date: Tue, 5 Aug 2025 17:30:57 -0700
From: Chris Li <chrisl@...nel.org>
To: Nhat Pham <nphamcs@...il.com>
Cc: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Kemeng Shi <shikemeng@...weicloud.com>, 
	Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>, 
	"Huang, Ying" <ying.huang@...ux.alibaba.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm, swap: prefer nonfull over free clusters

On Tue, Aug 5, 2025 at 5:03 PM Nhat Pham <nphamcs@...il.com> wrote:
>

> >
> > +       if (!(si->flags & SWP_PAGE_DISCARD)) {
> > +               ci = isolate_lock_cluster(si, &si->free_clusters);
> > +               if (ci) {
> > +                       found = alloc_swap_scan_cluster(si, ci, cluster_offset(si, ci),
> > +                                                       order, usage);
> > +                       if (found)
> > +                               goto done;
> > +               }
> > +       }
>
> Seems like this pattern is repeated a couple of places -
> isolate_lock_cluster from one of the lists, and if successful, then
> try to allocate (alloc_swap_scan_cluster) from it.
>
> Might be refactorable in a future clean up patch.
>
Yes, agree. I noticed that as well. Incidentally I am writing a RFC
patch to clean it up when I saw your email coming in. Another reason
to clean it up is that, isolate_lock_cluster() must be paired with
relocate_cluster(), otherwise we have a dangling cluster not in the
list. We'd better pair the isolate() and relocate() in the same
function for better visibility.

Chris