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Date: Wed, 17 Dec 2014 09:36:35 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Kamezawa Hiroyuki <kamezawa.hiroyu@...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
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
> +}
> +
> +/*
> + * 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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