From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 3F4AB6B007B for ; Wed, 8 Jun 2011 02:36:04 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp (unknown [10.0.50.72]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id 676143EE0BD for ; Wed, 8 Jun 2011 15:35:59 +0900 (JST) Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 4D15345DEA3 for ; Wed, 8 Jun 2011 15:35:59 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 33F5545DE83 for ; Wed, 8 Jun 2011 15:35:59 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 1EF4F1DB802C for ; Wed, 8 Jun 2011 15:35:59 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.240.81.145]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id CAD6C1DB803C for ; Wed, 8 Jun 2011 15:35:58 +0900 (JST) Date: Wed, 8 Jun 2011 15:29:01 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [BUGFIX][PATCH] memcg: fix behavior of per cpu charge cache draining. Message-Id: <20110608152901.f16b3e59.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110608144934.b5944a64.nishimura@mxp.nes.nec.co.jp> References: <20110608140518.0cd9f791.kamezawa.hiroyu@jp.fujitsu.com> <20110608144934.b5944a64.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Daisuke Nishimura Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , Ying Han , "hannes@cmpxchg.org" , Balbir Singh On Wed, 8 Jun 2011 14:49:34 +0900 Daisuke Nishimura wrote: > I have a few minor comments. > > On Wed, 8 Jun 2011 14:05:18 +0900 > KAMEZAWA Hiroyuki wrote: > > > This patch is made against mainline git tree. > > == > > From d1372da4d3c6f8051b5b1cf7b5e8b45a8094b388 Mon Sep 17 00:00:00 2001 > > From: KAMEZAWA Hiroyuki > > Date: Wed, 8 Jun 2011 13:51:11 +0900 > > Subject: [BUGFIX][PATCH] memcg: fix behavior of per cpu charge cache draining. > > > > For performance, memory cgroup caches some "charge" from res_counter > > into per cpu cache. This works well but because it's cache, > > it needs to be flushed in some cases. Typical cases are > > 1. when someone hit limit. > > 2. when rmdir() is called and need to charges to be 0. > > > > But "1" has problem. > > > > Recently, with large SMP machines, we see many kworker/%d:%d when > > memcg hit limit. It is because of flushing memcg's percpu cache. > > Bad things in implementation are > > > > a) it's called before calling try_to_free_mem_cgroup_pages() > > so, it's called immidiately when a task hit limit. > > (I thought it was better to avoid to run into memory reclaim. > > But it was wrong decision.) > > > > b) Even if a cpu contains a cache for memcg not related to > > a memcg which hits limit, drain code is called. > > > > This patch fixes a) and b) by > > > > A) delay calling of flushing until one run of try_to_free... > > Then, the number of calling is much decreased. > > B) check percpu cache contains a useful data or not. > > plus > > C) check asynchronous percpu draining doesn't run on the cpu. > > > > Reported-by: Ying Han > > Signed-off-by: KAMEZAWA Hiroyuki > > --- > > mm/memcontrol.c | 44 ++++++++++++++++++++++++++++---------------- > > 1 files changed, 28 insertions(+), 16 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index bd9052a..c22c0eb 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -359,7 +359,7 @@ enum charge_type { > > static void mem_cgroup_get(struct mem_cgroup *mem); > > static void mem_cgroup_put(struct mem_cgroup *mem); > > static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem); > > -static void drain_all_stock_async(void); > > +static void drain_all_stock_async(struct mem_cgroup *mem); > > > > static struct mem_cgroup_per_zone * > > mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid) > > @@ -1670,8 +1670,6 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > > victim = mem_cgroup_select_victim(root_mem); > > if (victim == root_mem) { > > loop++; > > - if (loop >= 1) > > - drain_all_stock_async(); > > if (loop >= 2) { > > /* > > * If we have not been able to reclaim > > @@ -1723,6 +1721,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > > return total; > > } else if (mem_cgroup_margin(root_mem)) > > return total; > > + drain_all_stock_async(root_mem); > > } > > return total; > > } > > @@ -1934,9 +1933,11 @@ struct memcg_stock_pcp { > > struct mem_cgroup *cached; /* this never be root cgroup */ > > unsigned int nr_pages; > > struct work_struct work; > > + unsigned long flags; > > +#define ASYNC_FLUSHING (0) > > }; > > static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); > > -static atomic_t memcg_drain_count; > > +static atomic_t memcg_drain_count; /* Indicates there is synchronous flusher */ > > > > /* > > * Try to consume stocked charge on this cpu. If success, one page is consumed > > @@ -1984,6 +1985,7 @@ static void drain_local_stock(struct work_struct *dummy) > > { > > struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock); > > drain_stock(stock); > > + clear_bit(ASYNC_FLUSHING, &stock->flags); > > } > > > > /* > > @@ -2006,28 +2008,38 @@ static void refill_stock(struct mem_cgroup *mem, unsigned int nr_pages) > > * Tries to drain stocked charges in other cpus. This function is asynchronous > > * and just put a work per cpu for draining localy on each cpu. Caller can > > * expects some charges will be back to res_counter later but cannot wait for > > - * it. > > + * it. This runs only when per-cpu stock contains information of memcg which > > + * is under specified root_mem and no other flush runs. > > */ > > -static void drain_all_stock_async(void) > > +static void drain_all_stock_async(struct mem_cgroup *root_mem) > > { > > int cpu; > > - /* This function is for scheduling "drain" in asynchronous way. > > - * The result of "drain" is not directly handled by callers. Then, > > - * if someone is calling drain, we don't have to call drain more. > > - * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if > > - * there is a race. We just do loose check here. > > + > > + /* > > + * If synchronous flushing (which flushes all cpus's cache) runs, > > + * do nothing. > > */ > > - if (atomic_read(&memcg_drain_count)) > > + if (unlikely(atomic_read(&memcg_drain_count))) > > return; > > - /* Notify other cpus that system-wide "drain" is running */ > > - atomic_inc(&memcg_drain_count); > > get_online_cpus(); > > for_each_online_cpu(cpu) { > > struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > > - schedule_work_on(cpu, &stock->work); > > + struct mem_cgroup *mem; > > + bool do_flush; > > + > > + rcu_read_lock(); > > Should this rcu_read_lock() be placed here ? IIUC, it's necessary only for css_is_ancestor(). > I thought rcu_read_lock() is required before getting a pointer to be acceseed. But hmm...at second thought.. 1. stock->cached is flushed before memcg is destroyed.. 2. force_empty()(before destroy memcg) and this function can do mutual execution by some lock. Then, it's safe to access stock->cached. Ok. I'll move this (with some comment) > > + mem = stock->cached; > > + if (!mem) { > > + rcu_read_unlock(); > > + continue; > > + } > > + do_flush = ((mem == root_mem) || > > + css_is_ancestor(&mem->css, &root_mem->css)); > > Adding "root_mem->use_hierarchy" is better to avoid flusing the cache as long as possible. > ok. here is v2. ==