From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753204Ab0HWDjo (ORCPT ); Sun, 22 Aug 2010 23:39:44 -0400 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:41088 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753116Ab0HWDjl (ORCPT ); Sun, 22 Aug 2010 23:39:41 -0400 Date: Mon, 23 Aug 2010 12:35:33 +0900 From: Daisuke Nishimura To: KAMEZAWA Hiroyuki 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, Daisuke Nishimura Subject: Re: [PATCH 2/5] memcg: use array and ID for quick look up Message-Id: <20100823123533.b75b99c5.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> 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 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". > @@ -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 ? Thanks, Daisuke Nishimura. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 91C6A6007D6 for ; Sun, 22 Aug 2010 23:39:00 -0400 (EDT) Date: Mon, 23 Aug 2010 12:35:33 +0900 From: Daisuke Nishimura Subject: Re: [PATCH 2/5] memcg: use array and ID for quick look up Message-Id: <20100823123533.b75b99c5.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki 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, Daisuke Nishimura List-ID: 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". > @@ -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 ? Thanks, Daisuke Nishimura. -- 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