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

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Message-ID: <20190530064453.GA110128@chrisdown.name>
Date:   Wed, 29 May 2019 23:44:53 -0700
From:   Chris Down <chris@...isdown.name>
To:     Michal Hocko <mhocko@...nel.org>
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

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.

(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.)