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Date:   Thu, 11 Apr 2019 18:35:00 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>, aryabinin@...tuozzo.com
Subject: Re: [RFC PATCH 0/2] mm/memcontrol: Finer-grained memory control

On 11.04.2019 17:55, Waiman Long wrote:
> On 04/11/2019 10:37 AM, Kirill Tkhai wrote:
>> On 10.04.2019 22:13, Waiman Long wrote:
>>> The current control mechanism for memory cgroup v2 lumps all the memory
>>> together irrespective of the type of memory objects. However, there
>>> are cases where users may have more concern about one type of memory
>>> usage than the others.
>>>
>>> We have customer request to limit memory consumption on anonymous memory
>>> only as they said the feature was available in other OSes like Solaris.
>>>
>>> To allow finer-grained control of memory, this patchset 2 new control
>>> knobs for memory controller:
>>>  - memory.subset.list for specifying the type of memory to be under control.
>>>  - memory.subset.high for the high limit of memory consumption of that
>>>    memory type.
>>>
>>> For simplicity, the limit is not hierarchical and applies to only tasks
>>> in the local memory cgroup.
>>>
>>> Waiman Long (2):
>>>   mm/memcontrol: Finer-grained control for subset of allocated memory
>>>   mm/memcontrol: Add a new MEMCG_SUBSET_HIGH event
>>>
>>>  Documentation/admin-guide/cgroup-v2.rst |  35 +++++++++
>>>  include/linux/memcontrol.h              |   8 ++
>>>  mm/memcontrol.c                         | 100 +++++++++++++++++++++++-
>>>  3 files changed, 142 insertions(+), 1 deletion(-)
>> CC Andrey.
>>
>> In Virtuozzo kernel we have similar functionality for limitation of page cache in a cgroup:
>>
>> https://github.com/OpenVZ/vzkernel/commit/8ceef5e0c07c7621fcb0e04ccc48a679dfeec4a4
> 
> It will be helpful to know the use case where you want to limit page
> cache usage. I have anonymous memory in mind when I compose this patch,
> but I make the mechanism more generic so that it can apply to other use
> cases as well.

We have distributed storage, and there are its daemons on every host.
There are replication factor 1:N, so the same block may be duplicated
on different hosts. They produce a lot of pagecache, but it is reused
not often (because of the above 1:N).

So, we want to limit pagecache, but do not limit anon memory. This
prevents global reclaim, and we found this improves our performance tests.

Kirill

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