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

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(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@jp.fujitsu.com>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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 ?

Thanks,
-Kame



>
>> +}
>> +
>> +/*
>> + * When a cpu is physically added, cpu<->node relationship is established
>> + * based on firmware info. We can catch the whole view when a new NODE_DATA()
>> + * coming up (a node is added).
>> + * If we don't update the info, pool->node will points to a not-online node
>> + * and the kernel will have allocation failure.
>> + *
>> + * Update wp_numa_possible_mask at online and clear it at offline.
>> + */
>> +void workqueue_node_register(int node)
>> +{
>> +	int cpu;
>> +
>> +	mutex_lock(&wq_pool_mutex);
>> +	for_each_possible_cpu(cpu)
>> +		workqueue_update_cpu_numa_affinity(cpu, node);
>> +	/* unbound workqueue will be updated when the 1st cpu comes up.*/
>> +	mutex_unlock(&wq_pool_mutex);
>> +}
>> +
>> +void workqueue_node_unregister(int node)
>> +{
>> +	struct worker_pool *pool;
>> +	int cpu;
>> +
>> +	mutex_lock(&wq_pool_mutex);
>> +	cpumask_clear(wq_numa_possible_cpumask[node]);
>> +	for_each_possible_cpu(cpu) {
>> +		if (node == cpu_to_node(cpu))
>> +			for_each_cpu_worker_pool(pool, cpu)
>> +				pool->node = NUMA_NO_NODE;
>> +	}
>> +	/*
>> +	 * unbound workqueue's per-node pwqs are already refleshed
>> +	 * by wq_update_unbound_numa() at CPU_DOWN_PREPARE of the last cpu
>> +	 * on this node, because all cpus of this node went down.
>> +	 * (see wq_calc_node_cpumask()). per-node unbound pwqs has been replaced
>> +	 * with wq->dfl_pwq, already.
>> +	 */
>> +	mutex_unlock(&wq_pool_mutex);
>> +}
>> +
>> +#endif
>>
>>   /*
>>    * Workqueues should be brought up before normal priority CPU notifiers.
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 9fab107..a0cb5c1 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1122,6 +1122,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>>   	 */
>>   	reset_node_present_pages(pgdat);
>>
>> +	/* Update workqueue's numa affinity info. */
>> +	workqueue_node_register(nid);
>> +
>>   	return pgdat;
>>   }
>>
>> @@ -1958,7 +1961,8 @@ void try_offline_node(int nid)
>>
>>   	if (check_and_unmap_cpu_on_node(pgdat))
>>   		return;
>> -
>> +	/* update workqueue's numa affinity info. */
>> +	workqueue_node_unregister(nid);
>>   	/*
>>   	 * all memory/cpu of this node are removed, we can offline this
>>   	 * node now.
>