From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755881AbcJFMF6 (ORCPT ); Thu, 6 Oct 2016 08:05:58 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36626 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751201AbcJFMFv (ORCPT ); Thu, 6 Oct 2016 08:05:51 -0400 Date: Thu, 6 Oct 2016 14:05:48 +0200 From: Michal Hocko To: Vladimir Davydov Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: memcontrol: use special workqueue for creating per-memcg caches Message-ID: <20161006120548.GH10570@dhcp22.suse.cz> References: <20161003120641.GC26768@dhcp22.suse.cz> <20161003123505.GA1862@esperanza> <20161003131930.GE26768@dhcp22.suse.cz> <20161004131417.GC1862@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161004131417.GC1862@esperanza> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 04-10-16 16:14:17, Vladimir Davydov wrote: [...] > >From 10f5f126800912c6a4b78a8b615138c1322694ad Mon Sep 17 00:00:00 2001 > From: Vladimir Davydov > Date: Sat, 1 Oct 2016 16:39:09 +0300 > Subject: [PATCH] mm: memcontrol: use special workqueue for creating per-memcg > caches > > Creating a lot of cgroups at the same time might stall all worker > threads with kmem cache creation works, because kmem cache creation is > done with the slab_mutex held. The problem was amplified by commits > 801faf0db894 ("mm/slab: lockless decision to grow cache") in case of > SLAB and 81ae6d03952c ("mm/slub.c: replace kick_all_cpus_sync() with > synchronize_sched() in kmem_cache_shrink()") in case of SLUB, which > increased the maximal time the slab_mutex can be held. > > To prevent that from happening, let's use a special ordered single > threaded workqueue for kmem cache creation. This shouldn't introduce any > functional changes regarding how kmem caches are created, as the work > function holds the global slab_mutex during its whole runtime anyway, > making it impossible to run more than one work at a time. By using a > single threaded workqueue, we just avoid creating a thread per each > work. Ordering is required to avoid a situation when a cgroup's work is > put off indefinitely because there are other cgroups to serve, in other > words to guarantee fairness. I am not sure an indefinit starving was possible but a fairness seems to be real AFAICS. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=172981 > Signed-off-by: Vladimir Davydov > Reported-by: Doug Smythies > Cc: Christoph Lameter > Cc: David Rientjes > Cc: Johannes Weiner > Cc: Joonsoo Kim > Cc: Michal Hocko > Cc: Pekka Enberg Acked-by: Michal Hocko > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4be518d4e68a..8d753d87ca37 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2175,6 +2175,8 @@ struct memcg_kmem_cache_create_work { > struct work_struct work; > }; > > +static struct workqueue_struct *memcg_kmem_cache_create_wq; > + > static void memcg_kmem_cache_create_func(struct work_struct *w) > { > struct memcg_kmem_cache_create_work *cw = > @@ -2206,7 +2208,7 @@ static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg, > cw->cachep = cachep; > INIT_WORK(&cw->work, memcg_kmem_cache_create_func); > > - schedule_work(&cw->work); > + queue_work(memcg_kmem_cache_create_wq, &cw->work); > } > > static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg, > @@ -5794,6 +5796,17 @@ static int __init mem_cgroup_init(void) > { > int cpu, node; > > +#ifndef CONFIG_SLOB > + /* > + * Kmem cache creation is mostly done with the slab_mutex held, > + * so use a special workqueue to avoid stalling all worker > + * threads in case lots of cgroups are created simultaneously. > + */ > + memcg_kmem_cache_create_wq = > + alloc_ordered_workqueue("memcg_kmem_cache_create", 0); > + BUG_ON(!memcg_kmem_cache_create_wq); > +#endif > + > hotcpu_notifier(memcg_cpu_hotplug_callback, 0); > > for_each_possible_cpu(cpu) -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id AB33F6B0069 for ; Thu, 6 Oct 2016 08:05:51 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id b80so7449660wme.1 for ; Thu, 06 Oct 2016 05:05:51 -0700 (PDT) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com. [74.125.82.68]) by mx.google.com with ESMTPS id cc10si16614619wjc.34.2016.10.06.05.05.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Oct 2016 05:05:50 -0700 (PDT) Received: by mail-wm0-f68.google.com with SMTP id b201so3204046wmb.1 for ; Thu, 06 Oct 2016 05:05:50 -0700 (PDT) Date: Thu, 6 Oct 2016 14:05:48 +0200 From: Michal Hocko Subject: Re: [PATCH 1/2] mm: memcontrol: use special workqueue for creating per-memcg caches Message-ID: <20161006120548.GH10570@dhcp22.suse.cz> References: <20161003120641.GC26768@dhcp22.suse.cz> <20161003123505.GA1862@esperanza> <20161003131930.GE26768@dhcp22.suse.cz> <20161004131417.GC1862@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161004131417.GC1862@esperanza> Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue 04-10-16 16:14:17, Vladimir Davydov wrote: [...] > >From 10f5f126800912c6a4b78a8b615138c1322694ad Mon Sep 17 00:00:00 2001 > From: Vladimir Davydov > Date: Sat, 1 Oct 2016 16:39:09 +0300 > Subject: [PATCH] mm: memcontrol: use special workqueue for creating per-memcg > caches > > Creating a lot of cgroups at the same time might stall all worker > threads with kmem cache creation works, because kmem cache creation is > done with the slab_mutex held. The problem was amplified by commits > 801faf0db894 ("mm/slab: lockless decision to grow cache") in case of > SLAB and 81ae6d03952c ("mm/slub.c: replace kick_all_cpus_sync() with > synchronize_sched() in kmem_cache_shrink()") in case of SLUB, which > increased the maximal time the slab_mutex can be held. > > To prevent that from happening, let's use a special ordered single > threaded workqueue for kmem cache creation. This shouldn't introduce any > functional changes regarding how kmem caches are created, as the work > function holds the global slab_mutex during its whole runtime anyway, > making it impossible to run more than one work at a time. By using a > single threaded workqueue, we just avoid creating a thread per each > work. Ordering is required to avoid a situation when a cgroup's work is > put off indefinitely because there are other cgroups to serve, in other > words to guarantee fairness. I am not sure an indefinit starving was possible but a fairness seems to be real AFAICS. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=172981 > Signed-off-by: Vladimir Davydov > Reported-by: Doug Smythies > Cc: Christoph Lameter > Cc: David Rientjes > Cc: Johannes Weiner > Cc: Joonsoo Kim > Cc: Michal Hocko > Cc: Pekka Enberg Acked-by: Michal Hocko > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4be518d4e68a..8d753d87ca37 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2175,6 +2175,8 @@ struct memcg_kmem_cache_create_work { > struct work_struct work; > }; > > +static struct workqueue_struct *memcg_kmem_cache_create_wq; > + > static void memcg_kmem_cache_create_func(struct work_struct *w) > { > struct memcg_kmem_cache_create_work *cw = > @@ -2206,7 +2208,7 @@ static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg, > cw->cachep = cachep; > INIT_WORK(&cw->work, memcg_kmem_cache_create_func); > > - schedule_work(&cw->work); > + queue_work(memcg_kmem_cache_create_wq, &cw->work); > } > > static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg, > @@ -5794,6 +5796,17 @@ static int __init mem_cgroup_init(void) > { > int cpu, node; > > +#ifndef CONFIG_SLOB > + /* > + * Kmem cache creation is mostly done with the slab_mutex held, > + * so use a special workqueue to avoid stalling all worker > + * threads in case lots of cgroups are created simultaneously. > + */ > + memcg_kmem_cache_create_wq = > + alloc_ordered_workqueue("memcg_kmem_cache_create", 0); > + BUG_ON(!memcg_kmem_cache_create_wq); > +#endif > + > hotcpu_notifier(memcg_cpu_hotplug_callback, 0); > > for_each_possible_cpu(cpu) -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org