From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751381AbdAYIat (ORCPT ); Wed, 25 Jan 2017 03:30:49 -0500 Received: from outbound-smtp03.blacknight.com ([81.17.249.16]:50552 "EHLO outbound-smtp03.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905AbdAYIar (ORCPT ); Wed, 25 Jan 2017 03:30:47 -0500 Date: Wed, 25 Jan 2017 08:30:38 +0000 From: Mel Gorman To: Andrew Morton Cc: Tejun Heo , Vlastimil Babka , Linux Kernel , Linux-MM , Hillf Danton , Jesper Dangaard Brouer Subject: [PATCH] mm, page_alloc: Use static global work_struct for draining per-cpu pages Message-ID: <20170125083038.rzb5f43nptmk7aed@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Mel Gorman --- mm/page_alloc.c | 41 +++++++++++++++++++++++------------------ 1 file changed, 23 insertions(+), 18 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e87508ffa759..da6be2a5ff7a 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); @@ -2351,7 +2355,6 @@ static void drain_local_pages_wq(struct work_struct *work) */ void drain_all_pages(struct zone *zone) { - struct work_struct __percpu *works; int cpu; /* @@ -2365,11 +2368,21 @@ void drain_all_pages(struct zone *zone) return; /* + * 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); + } + + /* * As this can be called from reclaim context, do not reenter reclaim. * An allocation failure can be handled, it's simply slower */ get_online_cpus(); - works = alloc_percpu_gfp(struct work_struct, GFP_ATOMIC); /* * We don't care about racing with CPU hotplug event @@ -2402,24 +2415,16 @@ 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)); + put_online_cpus(); + mutex_unlock(&pcpu_drain_mutex); } #ifdef CONFIG_HIBERNATION -- Mel Gorman SUSE Labs