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

[Lai Jiangshan <laijs@cn.fujitsu.com>]

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@jp.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.

>  		mutex_unlock(&wq_pool_mutex);
>  
>  		/* wait for per-cpu unbinding to finish */