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Date:   Tue, 18 Aug 2020 12:05:16 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     peterz@infradead.org
Cc:     Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
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        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [RFC PATCH 0/8] memcg: Enable fine-grained per process memory
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On Tue 18-08-20 11:59:10, Peter Zijlstra wrote:
> On Tue, Aug 18, 2020 at 11:26:17AM +0200, Michal Hocko wrote:
> > On Tue 18-08-20 11:14:53, Peter Zijlstra wrote:
> > > On Mon, Aug 17, 2020 at 10:08:23AM -0400, Waiman Long wrote:
> > > > Memory controller can be used to control and limit the amount of
> > > > physical memory used by a task. When a limit is set in "memory.high" in
> > > > a v2 non-root memory cgroup, the memory controller will try to reclaim
> > > > memory if the limit has been exceeded. Normally, that will be enough
> > > > to keep the physical memory consumption of tasks in the memory cgroup
> > > > to be around or below the "memory.high" limit.
> > > > 
> > > > Sometimes, memory reclaim may not be able to recover memory in a rate
> > > > that can catch up to the physical memory allocation rate. In this case,
> > > > the physical memory consumption will keep on increasing. 
> > > 
> > > Then slow down the allocator? That's what we do for dirty pages too, we
> > > slow down the dirtier when we run against the limits.
> > 
> > This is what we actually do. Have a look at mem_cgroup_handle_over_high.
> 
> But then how can it run-away like Waiman suggested?

As Chris mentioned in other reply. This functionality is quite new.
 
> /me goes look... and finds MEMCG_MAX_HIGH_DELAY_JIFFIES.

We can certainly tune a different backoff delays but I suspect this is
not the problem here.
 
> That's a fail... :-(

-- 
Michal Hocko
SUSE Labs