linux-kernel - Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc

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Message-Id: <1c1d70e3-4e45-b035-0e75-1b0f531c111b@linux.vnet.ibm.com>
Date:   Tue, 23 May 2017 15:05:08 -0500
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Bharata B Rao <bharata@...ux.vnet.ib>,
        Shailendra Singh <shailendras@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [Patch 2/2]: powerpc/hotplug/mm: Fix hot-add memory node assoc



On 05/23/2017 10:52 AM, Reza Arbab wrote:
> On Tue, May 23, 2017 at 10:15:44AM -0500, Michael Bringmann wrote:
>> +static void setup_nodes(void)
>> +{
>> +    int i, l = 32 /* MAX_NUMNODES */;
>> +
>> +    for (i = 0; i < l; i++) {
>> +        if (!node_possible(i)) {
>> +            setup_node_data(i, 0, 0);
>> +            node_set(i, node_possible_map);
>> +        }
>> +    }
>> +}
> 
> This seems to be a workaround for 3af229f2071f ("powerpc/numa: Reset node_possible_map to only node_online_map").

They may be related, but that commit is not a replacement.  The above patch ensures that
there are enough of the nodes initialized at startup to allow for memory hot-add into a
node that was not used at boot.  (See 'setup_node_data' function in 'numa.c'.)  That and
recording that the node was initialized.

I didn't see where any part of commit 3af229f2071f would touch the 'node_possible_map'
which is needed by 'numa.c' and 'workqueue.c'.  The nodemask created and updated by
'mem_cgroup_may_update_nodemask()' does not appear to be the same mask.

> 
> Balbir, you have a patchset which reverts it. Do you think that will be getting merged?
> 
> http://lkml.kernel.org/r/1479253501-26261-1-git-send-email-bsingharora@gmail.com
> (see patch 3/3)
> 

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com