linux-kernel - Re: [PATCH 1/2] workqueue: update numa affinity info at node hotplug

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Date:	Wed, 17 Dec 2014 13:56:29 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
CC:	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Ishimatsu, Yasuaki/石松 靖章" 
	<isimatu.yasuaki@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	"guz.fnst@...fujitsu.com" <guz.fnst@...fujitsu.com>
Subject: Re: [PATCH 1/2] workqueue: update numa affinity info at node hotplug

(2014/12/17 12:22), Kamezawa Hiroyuki wrote:
> (2014/12/17 10:36), Lai Jiangshan wrote:
>> On 12/17/2014 12:45 AM, Kamezawa Hiroyuki wrote:
>>> With node online/offline, cpu<->node relationship is established.
>>> Workqueue uses a info which was established at boot time but
>>> it may be changed by node hotpluging.
>>>
>>> Once pool->node points to a stale node, following allocation failure
>>> happens.
>>>    ==
>>>       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 updates per cpu workqueue pool's node affinity and
>>> updates wq_numa_possible_cpumask at node online/offline event.
>>> This update of mask is very important because it affects cpumasks
>>> and preferred node detection.
>>>
>>> Unbound workqueue's per node pool are updated by
>>> by wq_update_unbound_numa() at CPU_DOWN_PREPARE of the last cpu, by existing code.
>>> What important here is to avoid wrong node detection when a cpu get onlined.
>>> And it's handled by wq_numa_possible_cpumask update introduced by this patch.
>>>
>>> Changelog v3->v4:
>>>   - added workqueue_node_unregister
>>>   - clear wq_numa_possible_cpumask at node offline.
>>>   - merged a patch which handles per cpu pools.
>>>   - clear per-cpu-pool's pool->node at node offlining.
>>>   - set per-cpu-pool's pool->node at node onlining.
>>>   - dropped modification to get_unbound_pool()
>>>   - dropped per-cpu-pool handling at cpu online/offline.
>>>
>>> Reported-by:  Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>>> ---
>>>   include/linux/memory_hotplug.h |  3 +++
>>>   kernel/workqueue.c             | 58 +++++++++++++++++++++++++++++++++++++++++-
>>>   mm/memory_hotplug.c            |  6 ++++-
>>>   3 files changed, 65 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
>>> index 8f1a419..7b4a292 100644
>>> --- a/include/linux/memory_hotplug.h
>>> +++ b/include/linux/memory_hotplug.h
>>> @@ -270,4 +270,7 @@ extern void sparse_remove_one_section(struct zone *zone, struct mem_section *ms)
>>>   extern struct page *sparse_decode_mem_map(unsigned long coded_mem_map,
>>>                         unsigned long pnum);
>>>
>>> +/* update for workqueues */
>>> +void workqueue_node_register(int node);
>>> +void workqueue_node_unregister(int node);
>>>   #endif /* __LINUX_MEMORY_HOTPLUG_H */
>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>> index 6202b08..f6ad05a 100644
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -266,7 +266,7 @@ struct workqueue_struct {
>>>   static struct kmem_cache *pwq_cache;
>>>
>>>   static cpumask_var_t *wq_numa_possible_cpumask;
>>> -                    /* possible CPUs of each node */
>>> +                    /* PL: possible CPUs of each node */
>>>
>>>   static bool wq_disable_numa;
>>>   module_param_named(disable_numa, wq_disable_numa, bool, 0444);
>>> @@ -4563,6 +4563,62 @@ static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
>>>           WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>>>                             pool->attrs->cpumask) < 0);
>>>   }
>>> +#ifdef CONFIG_MEMORY_HOTPLUG
>>> +
>>> +static void workqueue_update_cpu_numa_affinity(int cpu, int node)
>>> +{
>>> +    struct worker_pool *pool;
>>> +
>>> +    if (node != cpu_to_node(cpu))
>>> +        return;
>>> +    cpumask_set_cpu(cpu, wq_numa_possible_cpumask[node]);
>>> +    for_each_cpu_worker_pool(pool, cpu)
>>> +        pool->node = node;
>>
>> Again, You need to check and update all the wq->numa_pwq_tbl[oldnode],
>> but in this patchset, the required information is lost and we can't find out oldnode.
>>
>>
>> cpus of oldnode, 16-31(online),48,56,64,72(offline,randomly assigned to the oldnode by numa_init_array())
>>
>> and then cpu#48 is allocated for newnode and online
>>
>> Now, the wq->numa_pwq_tbl[oldnode]'s cpumask still have cpu#48, and it may be scheduled to cpu#48.
>> See the information of my patch 4/5
>>
>
> That will not cause page allocation failure, right ? If so, it's out of scope of this patch 1/2.
>
> I think it's handled in patch 2/2, isn't it ?

Let me correct my words. Main purpose of this patch 1/2 is handling a case "node disappers" after boot.
And try to handle physicall node hotplug caes.

Changes of cpu<->node relationship at CPU_ONLINE is handled in patch 2/2.

Thanks,
-Kame



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