linux-kernel - Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting

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Message-ID: <20180816063509.GS32645@dhcp22.suse.cz>
Date:   Thu, 16 Aug 2018 08:35:09 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Andy Lutomirski <luto@...nel.org>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting

On Wed 15-08-18 13:20:44, Johannes Weiner wrote:
[...]
> This is completely backwards.
> 
> We respect the limits unless there is a *really* strong reason not
> to. The only situations I can think of is during OOM kills to avoid
> memory deadlocks and during packet reception for correctness issues
> (and because the network stack has its own way to reclaim memory).
> 
> Relying on some vague future allocations in the process's lifetime to
> fail in order to contain it is crappy and unreliable. And unwinding
> the stack allocation isn't too much complexity to warrant breaking the
> containment rules here, even if it were several steps. But it looks
> like it's nothing more than a 'goto free_stack'.
> 
> Please just fix this.

Thinking about it some more (sorry I should have done that in my
previous reply already) I do agree with Johannes. We should really back
off as soon as possible rather than rely on a future action because
this is quite subtle and prone to unexpected behavior.

-- 
Michal Hocko
SUSE Labs