linux-kernel - Re: [PATCH v2 2/3] mm: Force update of mem cgroup soft limit tree on usage excess

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Date:   Mon, 1 Mar 2021 08:39:23 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ying Huang <ying.huang@...el.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] mm: Force update of mem cgroup soft limit tree on
 usage excess

On Fri 26-02-21 16:56:28, Tim Chen wrote:
> 
> 
> On 2/26/21 12:52 AM, Michal Hocko wrote:
> 
> >>
> >> Michal,
> >>
> >> Let's take an extreme case where memcg 1 always generate the
> >> first event and memcg 2 generates the rest of 128*8-1 events
> >> and the pattern repeat.
> > 
> > I do not follow. Events are per-memcg, aren't they?
> > 	__this_cpu_read(memcg->vmstats_percpu->targets[target]);
> > 	[...]
> > 	__this_cpu_write(memcg->vmstats_percpu->targets[target], next);
> > 
> 
> You are right. My previous reasoning is incorrect as the sampling is done per memcg.
> I'll do some additional debugging on why memcg is not on the tree.

OK, thanks for the confirmation. I think we want to do 2 things. Remove
the soft limit specific threshold and stay with a single one and
recognize THPs.
-- 
Michal Hocko
SUSE Labs