From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue
Date: Thu, 3 Dec 2015 17:04:06 -0500 [thread overview]
Message-ID: <20151203220406.GA2630@mtj.duckdns.org> (raw)
In-Reply-To: <20151203210911.GZ17308@twins.programming.kicks-ass.net>
Hello, Peter.
On Thu, Dec 03, 2015 at 10:09:11PM +0100, Peter Zijlstra wrote:
> On Thu, Dec 03, 2015 at 03:56:32PM -0500, Tejun Heo wrote:
> > So, if I'm not mistaken, those are all marking tasks which can be
> > depended upon during memory reclaim and we do want to catch them all.
>
> Up to a point yes, these are things that want to be reliable during
> reclaim, but lacking memory reserves and usage bounds (which we
> discussed last at lsf/mm) these are just wanna-be.
Hmmm... even if buggy in that they can't guarantee forward-progress
even with access to the emergency pool, I think it makes sense to warn
them about creating an extra dependency which doesn't have access to
the emergency pool.
> > PF_MEMALLOC shouldn't depend on something which require memory to be
> > reclaimed to guarantee forward progress.
>
> PF_MEMALLOC basically avoids reclaim for any memory allocation while its
> set.
So, the assumption is that they're already on the reclaim path and
thus shouldn't recurse into it again.
> The thing is, even if your workqueue has WQ_MEM_RECLAIM set, it will not
> hit the mayday button until you're completely full flat out of memory.
It's more trigger-happy than that. It's timer based. If new worker
can't be created for a certain amount of time for whatever reason,
it'll summon the rescuer.
> At which point you're probably boned anyway, because, as per the above,
> all that code assumes there's _some_ memory to be had.
Not really. PF_MEMALLOC tasks have access to the emergency pool,
creating new workers doesn't, so this really is creating a dependency
which is qualitatively different.
> One solution is to always fail maybe_create_worker() when PF_MEMALLOC is
> set, thus always hitting the mayday button.
I'm not following. When PF_MEMALLOC is set where?
Thanks.
--
tejun
next prev parent reply other threads:[~2015-12-03 22:04 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-03 0:28 [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Tejun Heo
2015-12-03 0:28 ` [PATCH 2/2] workqueue: implement lockup detector Tejun Heo
2015-12-03 14:49 ` Tejun Heo
2015-12-03 17:50 ` Don Zickus
2015-12-03 19:43 ` Tejun Heo
2015-12-03 20:12 ` Ulrich Obergfell
2015-12-03 20:54 ` Tejun Heo
2015-12-04 8:02 ` Ingo Molnar
2015-12-04 16:52 ` Don Zickus
2015-12-04 13:19 ` Ulrich Obergfell
2015-12-07 19:06 ` [PATCH v2 " Tejun Heo
2015-12-07 21:38 ` Don Zickus
2015-12-07 21:39 ` Tejun Heo
2015-12-08 16:00 ` Don Zickus
2015-12-08 16:31 ` Tejun Heo
2015-12-03 9:33 ` [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Peter Zijlstra
2015-12-03 10:00 ` Peter Zijlstra
2015-12-03 14:48 ` Tejun Heo
2015-12-03 15:04 ` Peter Zijlstra
2015-12-03 15:06 ` Tejun Heo
2015-12-03 19:26 ` [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue Tejun Heo
2015-12-03 20:43 ` Peter Zijlstra
2015-12-03 20:56 ` Tejun Heo
2015-12-03 21:09 ` Peter Zijlstra
2015-12-03 22:04 ` Tejun Heo [this message]
2015-12-04 12:51 ` Peter Zijlstra
2015-12-07 15:58 ` Tejun Heo
2016-01-26 17:38 ` Thierry Reding
2016-01-28 10:12 ` Peter Zijlstra
2016-01-28 12:47 ` Thierry Reding
2016-01-28 12:48 ` Thierry Reding
2016-01-29 11:09 ` Tejun Heo
2016-01-29 15:17 ` Peter Zijlstra
2016-01-29 18:28 ` Tejun Heo
2016-01-29 10:59 ` [PATCH wq/for-4.5-fixes] workqueue: skip flush dependency checks for legacy workqueues Tejun Heo
2016-01-29 15:07 ` Thierry Reding
2016-01-29 18:32 ` Tejun Heo
2016-02-02 6:54 ` Archit Taneja
2016-03-10 15:12 ` [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue Adrian Hunter
2016-03-11 17:52 ` Tejun Heo
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