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

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Date:   Tue, 31 Jan 2017 16:00:29 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        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 Tue, Jan 31, 2017 at 07:52:37PM +0530, Anshuman Khandual wrote:
> At present, top_cpuset.mems_allowed is same as node_states[N_MEMORY] and it
> cannot be changed at the runtime. Maximum possible node_states[N_MEMORY]
> also gets reflected in top_cpuset.effective_mems interface. It prevents some
> one from removing or restricting memory placement which will be applicable
> system wide on a given memory node through cpuset mechanism which might be
> limiting. This solves the problem by enabling update_nodemask() function to
> accept changes to top_cpuset.mems_allowed as well. Once changed, it also
> updates the value of top_cpuset.effective_mems. Updates all it's task's
> mems_allowed nodemask as well. It calls cpuset_inc() to make sure cpuset
> is accounted for in the buddy allocator through cpusets_enabled() check.
> 

What's the point of allowing the root cpuset to be restricted?

-- 
Mel Gorman
SUSE Labs