From: Aaron Tomlin <atomlin@atomlin.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Aaron Tomlin <atomlin@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Christoph Lameter <cl@linux.com>,
tglx@linutronix.de, mingo@kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Phil Auld <pauld@redhat.com>
Subject: Re: [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too
Date: Thu, 17 Feb 2022 14:26:15 +0000 [thread overview]
Message-ID: <20220217142615.xqtiydixvnumyvei@ava.usersys.com> (raw)
In-Reply-To: <20220217124729.GA743618@lothringen>
On Thu 2022-02-17 13:47 +0100, Frederic Weisbecker wrote:
> So, to make sure I understand, the issue is that with nohz_full, we may
> well enter into the idle loop with the tick already stopped. We may also
> exit from idle without restarting the tick (again only with nohz_full). And
> so this can cause the vmstat to not be flushed upon idle entry. Right?
Hi Frederic,
Yes - this is exactly it.
> > A customer provided some evidence which indicates that the idle tick was
> > stopped; albeit, CPU-specific vmstat counters still remained populated.
> > Thus one can only assume quiet_vmstat() was not invoked on return to the
> > idle loop.
> >
> > Unfortunately, I suspect this divergence might erroneously prevent a
> > reclaim attempt by kswapd. If the number of zone specific free pages are
> > below their per-cpu drift value then zone_page_state_snapshot() is used to
> > compute a more accurate view of the aforementioned statistic.
> > Thus any task blocked on the NUMA node specific pfmemalloc_wait queue will
> > be unable to make significant progress via direct reclaim unless it is
> > killed after being woken up by kswapd (see throttle_direct_reclaim()).
> > That being said, eventually reclaim should give up if the conditions are
> > correct, no?
> Now if quiet_vmstat() isn't called, the vmstat_work should fix this later,
> right? Or does that happen too late perhaps?
If I understand correctly, in the context of nohz_full, since such work is
deferred, it will only be handled in a scenario when the periodic/or
scheduling-clock tick is enabled i.e. the timer was reprogrammed on exit
from idle.
Kind regards,
--
Aaron Tomlin
next prev parent reply other threads:[~2022-02-17 14:26 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-03 21:43 [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Aaron Tomlin
2022-02-03 22:22 ` Phil Auld
2022-02-16 14:34 ` Aaron Tomlin
2022-02-16 21:20 ` Phil Auld
2022-02-17 12:57 ` Frederic Weisbecker
2022-02-17 14:45 ` Aaron Tomlin
2022-02-17 12:47 ` Frederic Weisbecker
2022-02-17 14:26 ` Aaron Tomlin [this message]
2022-02-17 16:32 ` Frederic Weisbecker
2022-02-18 12:54 ` Aaron Tomlin
2022-02-19 15:46 ` Aaron Tomlin
2022-02-24 12:27 ` Marcelo Tosatti
2022-02-24 12:30 ` Marcelo Tosatti
2022-02-24 13:01 ` Aaron Tomlin
2022-02-24 12:37 ` Marcelo Tosatti
2022-02-24 13:00 ` Aaron Tomlin
2022-02-24 13:14 ` Marcelo Tosatti
2022-02-24 13:28 ` Aaron Tomlin
2022-02-24 13:40 ` Marcelo Tosatti
2022-02-24 13:44 ` Aaron Tomlin
2022-03-31 14:33 ` Aaron Tomlin
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