From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 994626B003D for ; Thu, 5 Feb 2009 21:08:24 -0500 (EST) Message-ID: <498B9B6C.3000808@cn.fujitsu.com> Date: Fri, 06 Feb 2009 10:07:40 +0800 From: Li Zefan MIME-Version: 1.0 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: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , "linux-kernel@vger.kernel.org" List-ID: > +/* > + * 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) -- 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