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Date: Fri, 06 Feb 2009 10:07:40 +0800 From: Li Zefan <lizf@...fujitsu.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> CC: "linux-mm@...ck.org" <linux-mm@...ck.org>, "balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>, "nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [RFC][PATCH] Reduce size of swap_cgroup by CSS 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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