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    SubjectRe: [PATCH v2 0/4] memcg: Low-limit reclaim
    On Wed, Apr 30, 2014 at 02:52:38PM -0700, Andrew Morton wrote:
    > On Mon, 28 Apr 2014 14:26:41 +0200 Michal Hocko <mhocko@suse.cz> wrote:
    >
    > > Hi,
    > > previous discussions have shown that soft limits cannot be reformed
    > > (http://lwn.net/Articles/555249/). This series introduces an alternative
    > > approach for protecting memory allocated to processes executing within
    > > a memory cgroup controller. It is based on a new tunable that was
    > > discussed with Johannes and Tejun held during the kernel summit 2013 and
    > > at LSF 2014.
    > >
    > > This patchset introduces such low limit that is functionally similar
    > > to a minimum guarantee. Memcgs which are under their lowlimit are not
    > > considered eligible for the reclaim (both global and hardlimit) unless
    > > all groups under the reclaimed hierarchy are below the low limit when
    > > all of them are considered eligible.
    >
    > Permitting containers to avoid global reclaim sounds rather worrisome.
    >
    > Fairness: won't it permit processes to completely protect their memory
    > while everything else in the system is getting utterly pounded? We
    > need to consider global-vs-memcg fairness as well as memcg-vs-memgc.

    Yes.

    > Security: can this feature be used to DoS the machine? Set up enough
    > hierarchies which are below their low limit and we risk memory
    > exhaustion and swap-thrashing and oom-killings for other processes.

    And yes.

    However, setting the low limit is a priviliged operation, so I don't
    see how you could do worse with it than with mlock, disabling swap
    etc.


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