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Subject: Re: [RFC PATCH 0/8] memcg: Enable fine-grained per process memory
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To:     Chris Down <chris@chrisdown.name>, peterz@infradead.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        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
References: <20200817140831.30260-1-longman@redhat.com>
 <20200818091453.GL2674@hirez.programming.kicks-ass.net>
 <20200818092737.GA148695@chrisdown.name>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <b11ce701-e824-793c-cc7f-4c3bbe08cf80@redhat.com>
Date:   Tue, 18 Aug 2020 15:30:02 -0400
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On 8/18/20 5:27 AM, Chris Down wrote:
> peterz@infradead.org writes:
>> 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.
>
> We already do that since v5.4. I'm wondering whether Waiman's customer 
> is just running with a too-old kernel without 0e4b01df865 ("mm, memcg: 
> throttle allocators when failing reclaim over memory.high") backported.
>
The fact is that we don't have that in RHEL8 yet and cgroup v2 is still 
not the default at the moment.

I am planning to backport the throttling patches to RHEL and hopefully 
can switch to use cgroup v2 soon.

Cheers,
Longman