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Subject: Re: [RFC PATCH] cgroup: introduce proportional protection on memcg
From:   Roman Gushchin <roman.gushchin@linux.dev>
In-Reply-To: <Yjx/3yi7BfH7wLPz@chrisdown.name>
Date:   Thu, 24 Mar 2022 09:23:44 -0700
Cc:     "zhaoyang.huang" <zhaoyang.huang@unisoc.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        ke wang <ke.wang@unisoc.com>,
        Zhaoyang Huang <huangzhaoyang@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org
Message-Id: <FE4CCCF9-CF08-424B-85D0-B5C1BA63329D@linux.dev>
References: <Yjx/3yi7BfH7wLPz@chrisdown.name>
To:     Chris Down <chris@chrisdown.name>
Precedence: bulk

It seems like what=E2=80=99s being proposed is an ability to express the pro=
tection in % of the current usage rather than an absolute number.
It=E2=80=99s an equivalent for something like a memory (reclaim) priority: e=
.g. a cgroup with 80% protection is _always_ reclaimed less aggressively tha=
n one with a 20% protection.

That said, I=E2=80=99m not a fan of this idea.
It might make sense in some reasonable range of usages, but if your workload=
 is simply leaking memory and growing indefinitely, protecting it seems like=
 a bad idea. And the first part can be easily achieved using an userspace to=
ol.

Thanks!

> On Mar 24, 2022, at 7:33 AM, Chris Down <chris@chrisdown.name> wrote:
>=20
> =EF=BB=BFI'm confused by the aims of this patch. We already have proportio=
nal reclaim for memory.min and memory.low, and memory.high is already "propo=
rtional" by its nature to drive memory back down behind the configured thres=
hold.
>=20
> Could you please be more clear about what you're trying to achieve and in w=
hat way the existing proportional reclaim mechanisms are insufficient for yo=
u?
>=20