linux-kernel - Re: [PATCH REBASED] mm, memcg: Make scan aggression always exclude protection

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Message-ID: <20190530065111.GC6703@dhcp22.suse.cz>
Date:   Thu, 30 May 2019 08:51:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Chris Down <chris@...isdown.name>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        Dennis Zhou <dennis@...nel.org>, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org, kernel-team@...com
Subject: Re: [PATCH REBASED] mm, memcg: Make scan aggression always exclude
 protection

On Wed 29-05-19 23:44:53, Chris Down wrote:
> Michal Hocko writes:
> > Maybe I am missing something so correct me if I am wrong but the new
> > calculation actually means that we always allow to scan even min
> > protected memcgs right?
> 
> We check if the memcg is min protected as a precondition for coming into
> this function at all, so this generally isn't possible. See the
> mem_cgroup_protected MEMCG_PROT_MIN check in shrink_node.

OK, that is the part I was missing, I got confused by checking the min
limit as well here. Thanks for the clarification. A comment would be
handy or do we really need to consider min at all?

> (Of course, it's possible we race with going within protection thresholds
> again, but this patch doesn't make that any better or worse than the
> previous situation.)

Yeah.

With the above clarified. The code the resulting code is much easier to
follow and the overal logic makes sense to me.

Acked-by: Michal Hocko <mhocko@...e.com>

-- 
Michal Hocko
SUSE Labs