linux-kernel - Re: [PATCH] mm/memcontrol: Don't increase effective low/min if no protection needed

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Date:   Tue, 18 Oct 2022 00:46:24 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Waiman Long <longman@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Chris Down <chris@...isdown.name>
Subject: Re: [PATCH] mm/memcontrol: Don't increase effective low/min if no
 protection needed

On Tue, Oct 11, 2022 at 07:04:32AM -1000, Tejun Heo <tj@...nel.org> wrote:
> Wouldn't it make sense to fix the test? With recursive_prot on, the cgroup
> actually is under low protection and it seems like the correct behavior is
> to report the low events accordingly.

It depends whether the there is a residual protection that the
memory.low=0 sibling can use (with memory_recursiveprot).

In the discussed LTP test, there should be no residual protection that
would justify the apparently misreported memory.low events. I.e. the
test is correct, the failure points to a subtle issue with distributing
residual protection among siblings.

Been there, (haven't) done that:
1) https://bugzilla.suse.com/show_bug.cgi?id=1196298
2) https://lore.kernel.org/r/20220325103118.GC2828@blackbody.suse.cz/

HTH,
Michal