linux-kernel - Re: [PATCH] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp

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Message-ID: <CAFULd4afM8UA7Xitd4d39+zAixFJjJUu9Yq0K0bHa9XN8aU_EA@mail.gmail.com>
Date: Sun, 22 Sep 2024 18:51:09 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>
Subject: Re: [PATCH] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()

On Fri, Sep 20, 2024 at 4:16 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Thu, Sep 19, 2024 at 10:14:05AM +0200, Uros Bizjak wrote:
> > --- a/fs/xfs/xfs_log_cil.c
> > +++ b/fs/xfs/xfs_log_cil.c
> > @@ -171,13 +171,12 @@ xlog_cil_insert_pcp_aggregate(
> >        * structures that could have a nonzero space_used.
> >        */
> >       for_each_cpu(cpu, &ctx->cil_pcpmask) {
> > -             int     old, prev;
> > +             int     old;
> >
> >               cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
> > +             old = READ_ONCE(cilpcp->space_used);
>
> Maybe it is just me, but this would probably look nicer if the cilpcp
> variable moved into the loop scope, and both were initialized at
> declaration time:
>
>                 struct xlog_cil_pcp     *cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
>                 int                     old = READ_ONCE(cilpcp->space_used);

No problem, I just tried to keep the number of changed lines as low as
possible. Some maintainers don't like functional and cosmetic changes
mixed together.

>
> >               do {
> > +             } while (!try_cmpxchg(&cilpcp->space_used, &old, 0));
>
> And this also looks a bit odd.  Again, probably preference, but a:
>
>                 while (!try_cmpxchg(&cilpcp->space_used, &old, 0))
>                         ;
>
> looks somewhat more normal (although still not pretty).

Yes, the alternative form is what some maintainers prefer.

> Sorry for not having anything more substantial to see, but the diff
> just looked a bit odd..

I'll prepare a v2 patch with the suggested changes.

Thanks,
Uros.