linux-kernel - Re: [RFC] mem-hotplug: shall we skip unmovable node when doing numa balance?

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Date:   Thu, 10 Nov 2016 09:07:22 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Xishi Qiu <qiuxishi@...wei.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tang Chen <tangchen@...fujitsu.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "robert.liu@...wei.com" <robert.liu@...wei.com>
Subject: Re: [RFC] mem-hotplug: shall we skip unmovable node when doing numa
 balance?

On Thu, Nov 10, 2016 at 11:17:03AM +0800, Xishi Qiu wrote:
> On 2016/11/9 19:58, Mel Gorman wrote:
> 
> > On Tue, Nov 08, 2016 at 12:43:17PM +0800, Xishi Qiu wrote:
> >> On mem-hotplug system, there is a problem, please see the following case.
> >>
> >> memtester xxG, the memory will be alloced on a movable node. And after numa
> >> balancing, the memory may be migrated to the other node, it may be a unmovable
> >> node. This will reduce the free memory of the unmovable node, and may be oom
> >> later.
> >>
> > 
> > How would it OOM later? It's movable memmory that is moving via
> > automatic NUMA balancing so at the very least it can be reclaimed. If
> > the memory is mlocked or unable to migrate then it's irrelevant if
> > automatic balancing put it there.
> > 
> 
> memtester will mlock the memory, so we can not reclaim, then maybe oom, right?
> So let the manager set some numa policies to prevent the above case, right?
> 

Deal with it using policies.

-- 
Mel Gorman
SUSE Labs