linux-kernel - Re: [PATCH v2] mm/swapfile:__swap_duplicate: drop redundant WRITE_ONCE on swap

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Date: Tue, 12 Mar 2024 07:14:24 +0800
From: Barry Song <21cnbao@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v2] mm/swapfile:__swap_duplicate: drop redundant
 WRITE_ONCE on swap_map for err cases

On Mon, Mar 11, 2024 at 10:37 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 21.02.24 22:08, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > The code is quite hard to read, we are still writing swap_map after
> > errors happen. Though the written value is as before,
> >
> >   has_cache = count & SWAP_HAS_CACHE;
> >   count &= ~SWAP_HAS_CACHE;
> >   [snipped]
> >   WRITE_ONCE(p->swap_map[offset], count | has_cache);
> >
> > It would be better to entirely drop the WRITE_ONCE for both
> > performance and readability.
> >
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > ---
> >   -v2: drop goto according to Andrew, Thanks!
> >
> >   mm/swapfile.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 556ff7347d5f..7cb6d9a2d51d 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -3320,7 +3320,8 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
> >       } else
> >               err = -ENOENT;                  /* unused swap entry */
> >
> > -     WRITE_ONCE(p->swap_map[offset], count | has_cache);
> > +     if (!err)
> > +             WRITE_ONCE(p->swap_map[offset], count | has_cache);
> >
> >   unlock_out:
> >       unlock_cluster_or_swap_info(p, ci);
>
> Maybe too late, but LGTM
>
> Reviewed-by: David Hildenbrand <david@...hat.com>

David, thanks!  Though it is probably too late as this one has been in
mm-stable for a long time.

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

Thanks
Barry