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Subject: Re: [PATCH v2 2/3] mm: Force update of mem cgroup soft limit tree on
 usage excess
To:     Michal Hocko <mhocko@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
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From:   Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <781634ee-ffb9-598d-fdb6-0ae6067448b7@linux.intel.com>
Date:   Fri, 26 Feb 2021 16:56:28 -0800
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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.

Tim