From: Marcelo Tosatti <mtosatti@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Minchan Kim <minchan@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>,
Nicolas Saenz Julienne <nsaenzju@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [patch v4] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu
Date: Mon, 7 Mar 2022 15:52:43 -0300 [thread overview]
Message-ID: <YiZUewMgjIt1as25@fuller.cnet> (raw)
In-Reply-To: <20220304163554.8872fe5d5a9d634f7a2884f5@linux-foundation.org>
On Fri, Mar 04, 2022 at 04:35:54PM -0800, Andrew Morton wrote:
> On Fri, 4 Mar 2022 13:29:31 -0300 Marcelo Tosatti <mtosatti@redhat.com> wrote:
>
> >
> > On systems that run FIFO:1 applications that busy loop
> > on isolated CPUs, executing tasks on such CPUs under
> > lower priority is undesired (since that will either
> > hang the system, or cause longer interruption to the
> > FIFO task due to execution of lower priority task
> > with very small sched slices).
> >
> > Commit d479960e44f27e0e52ba31b21740b703c538027c ("mm: disable LRU
> > pagevec during the migration temporarily") relies on
> > queueing work items on all online CPUs to ensure visibility
> > of lru_disable_count.
> >
> > However, its possible to use synchronize_rcu which will provide the same
> > guarantees (see comment this patch modifies on lru_cache_disable).
> >
> > Fixes:
> >
> > ...
> >
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -831,8 +831,7 @@ inline void __lru_add_drain_all(bool force_all_cpus)
> > for_each_online_cpu(cpu) {
> > struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
> >
> > - if (force_all_cpus ||
> > - pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
> > + if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) ||
>
> Please changelog this alteration?
It should be now. Are you OK with this changelog ?
(if not, please let me know what should be improved).
On systems that run FIFO:1 applications that busy loop,
any SCHED_OTHER task that attempts to execute
on such a CPU (such as work threads) will not
be scheduled, which leads to system hangs.
Commit d479960e44f27e0e52ba31b21740b703c538027c ("mm: disable LRU
pagevec during the migration temporarily") relies on
queueing work items on all online CPUs to ensure visibility
of lru_disable_count.
To fix this, replace the usage of work items with synchronize_rcu,
which provides the same guarantees:
Readers of lru_disable_count are protected by either disabling
preemption or rcu_read_lock:
preempt_disable, local_irq_disable [bh_lru_lock()]
rcu_read_lock [rt_spin_lock CONFIG_PREEMPT_RT]
preempt_disable [local_lock !CONFIG_PREEMPT_RT]
Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on
preempt_disable() regions of code. So any CPU which sees
lru_disable_count = 0 will have exited the critical
section when synchronize_rcu() returns.
Fixes:
...
Thanks.
next prev parent reply other threads:[~2022-03-07 18:53 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-22 16:01 [patch v2] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu Marcelo Tosatti
2022-02-22 16:07 ` [patch v3] " Marcelo Tosatti
2022-02-22 16:25 ` Nicolas Saenz Julienne
2022-03-04 1:03 ` Andrew Morton
2022-03-04 1:49 ` Paul E. McKenney
2022-03-04 15:08 ` Marcelo Tosatti
2022-03-04 16:02 ` Paul E. McKenney
2022-03-04 15:11 ` Marcelo Tosatti
2022-03-04 16:29 ` [patch v4] " Marcelo Tosatti
2022-03-05 0:35 ` Andrew Morton
2022-03-07 18:52 ` Marcelo Tosatti [this message]
2022-03-10 13:22 ` [patch v5] " Marcelo Tosatti
2022-03-11 2:23 ` Andrew Morton
2022-03-11 8:35 ` Sebastian Andrzej Siewior
2022-03-12 0:40 ` Andrew Morton
2022-03-12 20:39 ` Marcelo Tosatti
2022-03-13 9:23 ` Hillf Danton
2022-03-31 13:52 ` Borislav Petkov
2022-04-28 18:00 ` Marcelo Tosatti
2022-05-28 21:18 ` Andrew Morton
2022-05-28 22:54 ` Michael Larabel
2022-05-29 0:48 ` Michael Larabel
2022-06-19 12:14 ` Thorsten Leemhuis
2022-06-22 0:15 ` Andrew Morton
2022-03-05 4:33 ` [patch v4] " Paul E. McKenney
2022-03-08 17:41 ` Minchan Kim
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