linux-kernel - Re: [RFC PATCH 68/86] treewide: mm: remove cond

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Message-ID: <ZUuGCekSB727c61n@casper.infradead.org>
Date:   Wed, 8 Nov 2023 12:58:49 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
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Subject: Re: [RFC PATCH 68/86] treewide: mm: remove cond_resched()

On Wed, Nov 08, 2023 at 12:54:19AM -0800, Ankur Arora wrote:
> Yosry Ahmed <yosryahmed@...gle.com> writes:
> > On Tue, Nov 7, 2023 at 11:49 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> >> On 11/8/23 02:28, Sergey Senozhatsky wrote:
> >> > I'd personally prefer to have a comment explaining why we do that
> >> > spin_unlock/spin_lock sequence, which may look confusing to people.
> >>
> >> Wonder if it would make sense to have a lock operation that does the
> >> unlock/lock as a self-documenting thing, and maybe could also be optimized
> >> to first check if there's a actually a need for it (because TIF_NEED_RESCHED
> >> or lock is contended).
> >
> > +1, I was going to suggest this as well. It can be extended to other
> > locking types that disable preemption as well like RCU. Something like
> > spin_lock_relax() or something.
> 
> Good point. We actually do have exactly that: cond_resched_lock(). (And
> similar RW lock variants.)

That's a shame; I was going to suggest calling it spin_cycle() ...