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Date: Wed, 17 Dec 2014 12:22:54 +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 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 ?
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.
>
--
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