linux-kernel - Re: [PATCH 5/5] workqueue: retry on NUMA_NO_NODE when create

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Date:	Fri, 12 Dec 2014 11:05:24 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	"Gu, Zheng" <guz.fnst@...fujitsu.com>,
	tangchen <tangchen@...fujitsu.com>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 5/5] workqueue: retry on NUMA_NO_NODE when create_worker() fails

On Fri, Dec 12, 2014 at 5:19 AM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
> A pwq bound to a specified node might be last long or even forever after
> the node was offline.  Especially when this pwq has some back-to-back work
> items which requeue themselves and cause the pwq can't quit.
>
> This kinds of pwqs will cause their own pools busy and maybe create workers.
> This pools will fail on create_worker() since the node is offline.
>
> This case is extremely rare, but it is possible. And we hope create_worker()
> to be fault-tolerant in this case and other different cases when the node
> is lack of memory, for example, create_worker() can try to allocate memory
> from the whole system rather than only the target node, the most important
> thing is making some progress.
>
> So the solution is that, when the create_worker() fails on a specified node,
> it will retry with NUMA_NO_NODE for further allocation.

The code looks correct. But I don't think this issue depend on node offlining.
The allocation may also fail if node has no memory.
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