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Subject: Re: [PATCH] mem-hotplug: Don't clear the only node in new_node_page()
References: <1473044391.4250.19.camel@TP420>
 <d7393a3e-73a7-7923-bc32-d4dcbc6523f9@suse.cz>
 <20160912091811.GE14524@dhcp22.suse.cz>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <c144f768-7591-8bb8-4238-b3f1ecaf8b4b@suse.cz>
Date: Tue, 20 Sep 2016 10:31:31 +0200
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Sender: owner-linux-mm@kvack.org
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To: Michal Hocko <mhocko@suse.cz>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>, linux-mm <linux-mm@kvack.org>, jallen@linux.vnet.ibm.com, qiuxishi@huawei.com, iamjoonsoo.kim@lge.com, n-horiguchi@ah.jp.nec.com, rientjes@google.com, Andrew Morton <akpm@linux-foundation.org>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

On 09/12/2016 11:18 AM, Michal Hocko wrote:
> On Mon 05-09-16 16:18:29, Vlastimil Babka wrote:
>
>> Also OOM is skipped for __GFP_THISNODE
>> allocations, so we might also consider the same for nodemask-constrained
>> allocations?
>>
>> > The patch checks whether it is the last node on the system, and if it is, then
>> > don't clear the nid in the nodemask.
>>
>> I'd rather see the allocation not OOM, and rely on the fallback in
>> new_node_page() that doesn't have nodemask. But I suspect it might also make
>> sense to treat empty nodemask as something unexpected and put some WARN_ON
>> (instead of OOM) in the allocator.
>
> To be honest I am really not all that happy about 394e31d2ceb4
> ("mem-hotplug: alloc new page from a nearest neighbor node when
> mem-offline") and find it a bit fishy. I would rather re-iterate that
> patch rather than build new hacks on top.

OK, IIRC I suggested the main idea of clearing the current node from nodemask 
and relying on nodelist to get us the other nodes sorted by their distance. 
Which I thought was an easy way to get to the theoretically optimal result. How 
would you rewrite it then? (but note that the fix is already mainline).

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