linux-kernel - Re: [RFC PATCH] cgroup: introduce dynamic protection for memcg

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Message-ID: <YkwxNaJIg6ptJOYT@dhcp22.suse.cz>
Date:   Tue, 5 Apr 2022 14:08:21 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        cgroups mailinglist <cgroups@...r.kernel.org>,
        Ke Wang <ke.wang@...soc.com>
Subject: Re: [RFC PATCH] cgroup: introduce dynamic protection for memcg

On Mon 04-04-22 21:14:40, Zhaoyang Huang wrote:
[...]
> Please be noticed that this patch DOES protect the memcg when external
> pressure is 1GB as fixed low does.

This is getting more and more confusing (at least to me). Could you
describe the behavior of the reclaim for the following setups/situations?

a) mostly reclaiming a clean page cache - via kswapd
b) same as above but the direct reclaim is necessary but very
   lightweight
c) direct reclaim makes fwd progress but not enough to satisfy the
   allocation request (so the reclaim has to be retried)
d) direct reclaim not making progress and low limit protection is
   ignored.

Say we have several memcgs and only some have low memory protection
configured. What is the user observable state of the protected group and
when and how much the protection can be updated?

I think it would be also helpful to describe the high level semantic of
this feature.

> Besides, how does the admin decide
> the exact number of low/min if it expand from small to even xGB in a
> quick changing scenario?

This is not really related, is it? There are different ways to tune for
the protection.

[...]
-- 
Michal Hocko
SUSE Labs