From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757657AbZBFCIc (ORCPT ); Thu, 5 Feb 2009 21:08:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752794AbZBFCIW (ORCPT ); Thu, 5 Feb 2009 21:08:22 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:60220 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751384AbZBFCIW (ORCPT ); Thu, 5 Feb 2009 21:08:22 -0500 Message-ID: <498B9B6C.3000808@cn.fujitsu.com> Date: Fri, 06 Feb 2009 10:07:40 +0800 From: Li Zefan User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: KAMEZAWA Hiroyuki CC: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH] Reduce size of swap_cgroup by CSS ID References: <20090205185959.7971dee4.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090205185959.7971dee4.kamezawa.hiroyu@jp.fujitsu.com> 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 > +/* > + * A helper function to get mem_cgroup from ID. must be called under > + * rcu_read_lock(). Because css_tryget() is called under this, css_put > + * should be called later. > + */ > +static struct mem_cgroup *mem_cgroup_lookup_get(unsigned short id) > +{ > + struct cgroup_subsys_state *css; > + > + /* ID 0 is unused ID */ > + if (!id) > + return NULL; > + css = css_lookup(&mem_cgroup_subsys, id); > + if (css && css_tryget(css)) > + return container_of(css, struct mem_cgroup, css); > + return NULL; > +} the returned mem_cgroup needn't be protected by rcu_read_lock(), so I think this is better: rcu_read_lock(); css = css_lookup(&mem_cgroup_subsys, id); rcu_read_unlock(); and no lock is needed when calling mem_cgroup_lookup_get(). > * Returns old value at success, NULL at failure. > * (Of course, old value can be NULL.) > */ > -struct mem_cgroup *swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem) > +unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id) kernel-doc needs to be updated > * lookup_swap_cgroup - lookup mem_cgroup tied to swap entry > * @ent: swap entry to be looked up. > * > - * Returns pointer to mem_cgroup at success. NULL at failure. > + * Returns CSS ID of mem_cgroup at success. NULL at failure. s/NULL/0/ > */ > -struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent) > +unsigned short lookup_swap_cgroup(swp_entry_t ent)