From bd233f538d51c2cae6f0bfc2cf7f0960e1683b8a Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Fri, 24 Feb 2017 14:56:56 -0800 Subject: [PATCH] mm, page_alloc: use static global work_struct for draining per-cpu pages As suggested by Vlastimil Babka and Tejun Heo, this patch uses a static work_struct to co-ordinate the draining of per-cpu pages on the workqueue. Only one task can drain at a time but this is better than the previous scheme that allowed multiple tasks to send IPIs at a time. One consideration is whether parallel requests should synchronise against each other. This patch does not synchronise for a global drain as the common case for such callers is expected to be multiple parallel direct reclaimers competing for pages when the watermark is close to min. Draining the per-cpu list is unlikely to make much progress and serialising the drain is of dubious merit. Drains are synchonrised for callers such as memory hotplug and CMA that care about the drain being complete when the function returns. Link: http://lkml.kernel.org/r/20170125083038.rzb5f43nptmk7aed@techsingularity.net Signed-off-by: Mel Gorman Suggested-by: Tejun Heo Suggested-by: Vlastimil Babka Acked-by: Vlastimil Babka Acked-by: Hillf Danton Cc: Jesper Dangaard Brouer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 40 ++++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 18 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 46c30fa26acd..41985aa4672d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -92,6 +92,10 @@ EXPORT_PER_CPU_SYMBOL(_numa_mem_); int _node_numa_mem_[MAX_NUMNODES]; #endif +/* work_structs for global per-cpu drains */ +DEFINE_MUTEX(pcpu_drain_mutex); +DEFINE_PER_CPU(struct work_struct, pcpu_drain); + #ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY volatile unsigned long latent_entropy __latent_entropy; EXPORT_SYMBOL(latent_entropy); @@ -2360,7 +2364,6 @@ static void drain_local_pages_wq(struct work_struct *work) */ void drain_all_pages(struct zone *zone) { - struct work_struct __percpu *works; int cpu; /* @@ -2373,7 +2376,16 @@ void drain_all_pages(struct zone *zone) if (current->flags & PF_WQ_WORKER) return; - works = alloc_percpu_gfp(struct work_struct, GFP_ATOMIC); + /* + * Do not drain if one is already in progress unless it's specific to + * a zone. Such callers are primarily CMA and memory hotplug and need + * the drain to be complete when the call returns. + */ + if (unlikely(!mutex_trylock(&pcpu_drain_mutex))) { + if (!zone) + return; + mutex_lock(&pcpu_drain_mutex); + } /* * We don't care about racing with CPU hotplug event @@ -2406,23 +2418,15 @@ void drain_all_pages(struct zone *zone) cpumask_clear_cpu(cpu, &cpus_with_pcps); } - if (works) { - for_each_cpu(cpu, &cpus_with_pcps) { - struct work_struct *work = per_cpu_ptr(works, cpu); - INIT_WORK(work, drain_local_pages_wq); - schedule_work_on(cpu, work); - } - for_each_cpu(cpu, &cpus_with_pcps) - flush_work(per_cpu_ptr(works, cpu)); - } else { - for_each_cpu(cpu, &cpus_with_pcps) { - struct work_struct work; - - INIT_WORK(&work, drain_local_pages_wq); - schedule_work_on(cpu, &work); - flush_work(&work); - } + for_each_cpu(cpu, &cpus_with_pcps) { + struct work_struct *work = per_cpu_ptr(&pcpu_drain, cpu); + INIT_WORK(work, drain_local_pages_wq); + schedule_work_on(cpu, work); } + for_each_cpu(cpu, &cpus_with_pcps) + flush_work(per_cpu_ptr(&pcpu_drain, cpu)); + + mutex_unlock(&pcpu_drain_mutex); } #ifdef CONFIG_HIBERNATION -- 2.20.1