From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 31ACC6B03F1 for ; Mon, 23 Aug 2010 20:33:13 -0400 (EDT) Date: Tue, 24 Aug 2010 09:19:20 +0900 From: Daisuke Nishimura Subject: Re: [PATCH 2/5] memcg: use array and ID for quick look up Message-Id: <20100824091920.181932e0.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20100824085111.6acf8881.kamezawa.hiroyu@jp.fujitsu.com> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820185917.87876cb0.kamezawa.hiroyu@jp.fujitsu.com> <20100823123533.b75b99c5.nishimura@mxp.nes.nec.co.jp> <20100824085111.6acf8881.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: > > > @@ -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. > Ah, I see. Thank you for your explanation. 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