From: Peter Zijlstra <peterz@infradead.org>
To: "Sebastian A. Siewior" <bigeasy@linutronix.de>
Cc: "Ahmed S. Darwish" <a.darwish@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
linux-mm@kvack.org
Subject: Re: [PATCH v1 02/25] mm/swap: Don't abuse the seqcount latching API
Date: Fri, 22 May 2020 18:23:18 +0200 [thread overview]
Message-ID: <20200522162318.GV317569@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200522151705.vwfua5a4lhzcagea@linutronix.de>
On Fri, May 22, 2020 at 05:17:05PM +0200, Sebastian A. Siewior wrote:
> On 2020-05-22 16:57:07 [+0200], Peter Zijlstra wrote:
> > > @@ -725,21 +735,48 @@ void lru_add_drain_all(void)
> > > if (WARN_ON(!mm_percpu_wq))
> > > return;
> > >
> >
> > > + this_gen = READ_ONCE(lru_drain_gen);
> > > + smp_rmb();
> >
> > this_gen = smp_load_acquire(&lru_drain_gen);
> > >
> > > mutex_lock(&lock);
> > >
> > > /*
> > > + * (C) Exit the draining operation if a newer generation, from another
> > > + * lru_add_drain_all(), was already scheduled for draining. Check (A).
> > > */
> > > + if (unlikely(this_gen != lru_drain_gen))
> > > goto done;
> > >
> >
> > > + WRITE_ONCE(lru_drain_gen, lru_drain_gen + 1);
> > > + smp_wmb();
> >
> > You can leave this smp_wmb() out and rely on the smp_mb() implied by
> > queue_work_on()'s test_and_set_bit().
>
> This is to avoid smp_store_release() ?
store_release would have the barrier on the other end. If you read the
comments (I so helpfully cut out) you'll see it wants to order against
later stores, not ealier.
next prev parent reply other threads:[~2020-05-22 16:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 21:45 [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 02/25] mm/swap: Don't abuse the seqcount latching API Ahmed S. Darwish
2020-05-20 11:24 ` Hillf Danton
2020-05-20 12:22 ` Konstantin Khlebnikov
2020-05-20 13:05 ` Peter Zijlstra
2020-05-22 14:57 ` Peter Zijlstra
2020-05-22 15:17 ` Sebastian A. Siewior
2020-05-22 16:23 ` Peter Zijlstra [this message]
2020-05-25 15:24 ` Ahmed S. Darwish
2020-05-25 15:45 ` Peter Zijlstra
2020-05-25 16:10 ` John Ogness
[not found] ` <20200827114044.11173-1-a.darwish@linutronix.de>
2020-08-27 11:40 ` [PATCH v1 2/8] mm/swap: Do not abuse the seqcount_t " Ahmed S. Darwish
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