linux-kernel - Re: [RFC PATCH] cgroup: introduce proportional protection on memcg

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Date:   Thu, 24 Mar 2022 09:23:44 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Chris Down <chris@...isdown.name>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        ke wang <ke.wang@...soc.com>,
        Zhaoyang Huang <huangzhaoyang@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH] cgroup: introduce proportional protection on memcg

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

That said, I’m 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 tool.

Thanks!

> On Mar 24, 2022, at 7:33 AM, Chris Down <chris@...isdown.name> wrote:
> 
> I'm confused by the aims of this patch. We already have proportional reclaim for memory.min and memory.low, and memory.high is already "proportional" by its nature to drive memory back down behind the configured threshold.
> 
> Could you please be more clear about what you're trying to achieve and in what way the existing proportional reclaim mechanisms are insufficient for you?
>