linux-kernel - Re: [RFC] cpuset: Enable changing of top_cpuset's mems

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Message-ID: <20170201085326.GE5977@dhcp22.suse.cz>
Date:   Wed, 1 Feb 2017 09:53:26 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, minchan@...nel.org,
        aneesh.kumar@...ux.vnet.ibm.com, bsingharora@...il.com,
        srikar@...ux.vnet.ibm.com, haren@...ux.vnet.ibm.com,
        jglisse@...hat.com, dave.hansen@...el.com, dan.j.williams@...el.com
Subject: Re: [RFC] cpuset: Enable changing of top_cpuset's mems_allowed
 nodemask

On Wed 01-02-17 13:01:24, Anshuman Khandual wrote:
[...]
> More importantly it also extends the cpuset memory restriction feature
> to the logical completion without adding any regressions for the
> existing use cases. Then why not do this ? Does it add any overhead ?

Maybe it doesn't add any overhead but it just breaks the cgroups
expectation that the root cgroup covers the full resource set. No cgroup
controller allows to set limits on the root cgroup. So all this looks
like an abuse of the interface.

I haven't read the full series yet but this particular change looks like
a nogo to me.

-- 
Michal Hocko
SUSE Labs