linux-kernel - Re: [PATCH v2 2/2] mm/cgroup: delay soft limit data allocation

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Message-ID: <20170223190313.GB6088@cmpxchg.org>
Date:   Thu, 23 Feb 2017 14:03:13 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/cgroup: delay soft limit data allocation

On Thu, Feb 23, 2017 at 04:31:07PM +0100, Michal Hocko wrote:
> On Thu 23-02-17 14:36:39, Laurent Dufour wrote:
> > Until a soft limit is set to a cgroup, the soft limit data are useless
> > so delay this allocation when a limit is set.
> 
> Hmm, I am still undecided whether this is actually worth it. On one hand
> distribution kernels tend to have quite large NUMA_SHIFT (e.g. SLES has
> NUMA_SHIFT=10 and then we will save 8kB+12kB which is not hell of a lot
> but always good if we can save that, especially for a rarely used
> feature. The code grown on the other hand (it was in __init section
> previously) which is a minus, on the other hand.
> 
> What do you think Johannes?

Hohumm, saving 5 pages on a NUMA machine vs. the additional complexity
and the increased risk of memory problems when somebody sets up a soft
limit after some uptime... I don't think I can give a strong yes or no
on this one, so inertia wins for me; I'd just leave it alone.