linux-kernel - Re: [PATCH 2/4] workqueue: update per-cpu workqueue's node affinity at,online-offline

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Date:	Tue, 16 Dec 2014 16:25:10 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
CC:	<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>
Subject: Re: [PATCH 2/4] workqueue: update per-cpu workqueue's node affinity
 at,online-offline

(2014/12/16 14:32), Lai Jiangshan wrote:
> On 12/15/2014 07:16 PM, Kamezawa Hiroyuki wrote:
>> The percpu workqueue pool are persistend and never be freed.
>> But cpu<->node relationship can be changed by cpu hotplug and pool->node
>> can point to an offlined node.
>>
>> If pool->node points to an offlined node,
>> following allocation failure can happen.
>>      ==
>>       SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
>>        cache: kmalloc-192, object size: 192, buffer size: 192, default
>> order:
>>      1, min order: 0
>>        node 0: slabs: 6172, objs: 259224, free: 245741
>>        node 1: slabs: 3261, objs: 136962, free: 127656
>>      ==
>>
>> This patch clears per-cpu workqueue pool's node affinity at
>> cpu offlining and restore it at cpu onlining.
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>> ---
>>   kernel/workqueue.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>> index 7809154..2fd0bd7 100644
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -4586,6 +4586,11 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
>>   	case CPU_DOWN_FAILED:
>>   	case CPU_ONLINE:
>>   		mutex_lock(&wq_pool_mutex);
>> +		/*
>> +		 * now cpu <-> node info is established. update numa node
>> +		 */
>> +		for_each_cpu_worker_pool(pool, cpu)
>> +			pool->node = cpu_to_node(cpu);
>>
>>   		for_each_pool(pool, pi) {
>>   			mutex_lock(&pool->attach_mutex);
>> @@ -4619,6 +4624,7 @@ static int workqueue_cpu_down_callback(struct notifier_block *nfb,
>>   	int cpu = (unsigned long)hcpu;
>>   	struct work_struct unbind_work;
>>   	struct workqueue_struct *wq;
>> +	struct worker_pool *pool;
>>
>>   	switch (action & ~CPU_TASKS_FROZEN) {
>>   	case CPU_DOWN_PREPARE:
>> @@ -4626,10 +4632,13 @@ static int workqueue_cpu_down_callback(struct notifier_block *nfb,
>>   		INIT_WORK_ONSTACK(&unbind_work, wq_unbind_fn);
>>   		queue_work_on(cpu, system_highpri_wq, &unbind_work);
>>
>> -		/* update NUMA affinity of unbound workqueues */
>>   		mutex_lock(&wq_pool_mutex);
>> +		/* update NUMA affinity of unbound workqueues */
>>   		list_for_each_entry(wq, &workqueues, list)
>>   			wq_update_unbound_numa(wq, cpu, false);
>> +		/* clear per-cpu workqueues's numa affinity. */
>> +		for_each_cpu_worker_pool(pool, cpu)
>> +			pool->node = NUMA_NO_NODE; /* restored at online */
>
>
> If the node is still online, it is better to keep the original pool->node.
>

Hm, ok, drop this code.  or moving all to node online event handler.

Thanks,
-Kame


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