From: Rik van Riel <riel@fb.com>
To: "shakeelb@google.com" <shakeelb@google.com>
Cc: Kernel Team <Kernel-team@fb.com>,
"dan.carpenter@oracle.com" <dan.carpenter@oracle.com>,
"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
Date: Tue, 3 Aug 2021 14:34:23 +0000 [thread overview]
Message-ID: <f3bc8b44d58a5e63178dee40f9c119cfc8bf669b.camel@fb.com> (raw)
In-Reply-To: <CALvZod5JmcSpym6oXMXEUXEq2u13SVLRaVGPg84ubeYZt-6w_g@mail.gmail.com>
On Tue, 2021-07-27 at 09:51 -0700, Shakeel Butt wrote:
> On Mon, Jul 26, 2021 at 8:19 AM Rik van Riel <riel@fb.com> wrote:
> >
> > On Mon, 2021-07-26 at 11:00 -0400, Johannes Weiner wrote:
> > >
> > > __mem_cgroup_threshold() indeed holds the rcu lock. In addition,
> > > the
> > > thresholding code is invoked during stat changes, and those
> > > contexts
> > > have irqs disabled as well. If the lock breaking occurs inside
> > > the
> > > flush function, it will result in a sleep from an atomic context.
> > >
> > > Use the irsafe flushing variant in mem_cgroup_usage() to fix this
> >
> > While this fix is necessary, in the long term I think we may
> > want some sort of redesign here, to make sure the irq safe
> > version does not spin long times trying to get the statistics
> > off some other CPU.
> >
> > I have seen a number of soft (IIRC) lockups deep inside the
> > bowels of cgroup_rstat_flush_irqsafe, with the function taking
> > multiple seconds to complete.
>
> Can you please share a bit more detail on this lockup? I am wondering
> if this was due to the flush not happening more often and thus the
> update tree is large or if there are too many concurrent flushes
> happening.
I was not logged into any system while it happened, but
only found it later in the logs.
I suspect your explanation is the reason why it happened,
though.
next prev parent reply other threads:[~2021-08-03 14:34 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 15:00 [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code Johannes Weiner
2021-07-26 15:08 ` Chris Down
2021-07-26 15:16 ` Rik van Riel
2021-07-27 16:51 ` Shakeel Butt
2021-08-03 14:34 ` Rik van Riel [this message]
2021-07-26 20:32 ` Michal Hocko
2021-07-27 16:59 ` Shakeel Butt
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