Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753414Ab0HWX4N (ORCPT ); Mon, 23 Aug 2010 19:56:13 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:47203 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753158Ab0HWX4L (ORCPT ); Mon, 23 Aug 2010 19:56:11 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 24 Aug 2010 08:51:11 +0900 From: KAMEZAWA Hiroyuki To: Daisuke Nishimura Cc: linux-mm@kvack.org, "balbir@linux.vnet.ibm.com" , gthelen@google.com, m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , kamezawa.hiroyuki@gmail.com Subject: Re: [PATCH 2/5] memcg: use array and ID for quick look up Message-Id: <20100824085111.6acf8881.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100823123533.b75b99c5.nishimura@mxp.nes.nec.co.jp> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> <20100823123533.b75b99c5.nishimura@mxp.nes.nec.co.jp> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2596 Lines: 86 On Mon, 23 Aug 2010 12:35:33 +0900 Daisuke Nishimura wrote: > Hi, > > > +/* 0 is unused */ > > +static atomic_t mem_cgroup_num; > > +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1) > > +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly; > > + > > +/* Must be called under rcu_read_lock */ > > +static struct mem_cgroup *id_to_memcg(unsigned short id) > > +{ > > + struct mem_cgroup *ret; > > + /* see mem_cgroup_free() */ > > + ret = rcu_dereference_check(mem_cgroups[id], rch_read_lock_held()); > > + if (likely(ret && ret->valid)) > > + return ret; > > + return NULL; > > +} > > + > I prefer "mem" to "ret". > Hmm, ok. > > @@ -2231,7 +2244,7 @@ __mem_cgroup_commit_charge_swapin(struct > > > > id = swap_cgroup_record(ent, 0); > > rcu_read_lock(); > > - memcg = mem_cgroup_lookup(id); > > + memcg = id_to_memcg(id); > > if (memcg) { > > /* > > * This recorded memcg can be obsolete one. So, avoid > > @@ -2240,9 +2253,10 @@ __mem_cgroup_commit_charge_swapin(struct > > if (!mem_cgroup_is_root(memcg)) > > res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > mem_cgroup_swap_statistics(memcg, false); > > + rcu_read_unlock(); > > mem_cgroup_put(memcg); > > - } > > - rcu_read_unlock(); > > + } else > > + rcu_read_unlock(); > > } > > /* > > * At swapin, we may charge account against cgroup which has no tasks. > > @@ -2495,7 +2509,7 @@ void mem_cgroup_uncharge_swap(swp_entry_ > > > > id = swap_cgroup_record(ent, 0); > > rcu_read_lock(); > > - memcg = mem_cgroup_lookup(id); > > + memcg = id_to_memcg(id); > > if (memcg) { > > /* > > * We uncharge this because swap is freed. > > @@ -2504,9 +2518,10 @@ void mem_cgroup_uncharge_swap(swp_entry_ > > if (!mem_cgroup_is_root(memcg)) > > res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > mem_cgroup_swap_statistics(memcg, false); > > + rcu_read_unlock(); > > mem_cgroup_put(memcg); > > - } > > - rcu_read_unlock(); > > + } else > > + rcu_read_unlock(); > > } > > > > /** > Could you explain why we need rcu_read_unlock() before mem_cgroup_put() ? > I suspect that it's because mem_cgroup_put() can free the memcg, but do we > need mem->valid then ? > mem_cgroup_put() may call synchronize_rcu(). So, we have to unlock before it. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/