Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756998Ab0HFEhy (ORCPT ); Fri, 6 Aug 2010 00:37:54 -0400 Received: from smtp-out.google.com ([216.239.44.51]:4548 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917Ab0HFEhv convert rfc822-to-8bit (ORCPT ); Fri, 6 Aug 2010 00:37:51 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:from:date:message-id: subject:to:cc:content-type:content-transfer-encoding:x-system-of-record; b=k3eH0lNZnVWcT2VkJDz7svOv9D1Tk90QOeYmFN68vrnlo41s1Nq7VWX91Ms3pFIAy zWwJj2HMsrK4SMo0Z3oEg== MIME-Version: 1.0 In-Reply-To: <20100806131053.411dce6d.kamezawa.hiroyu@jp.fujitsu.com> References: <20100805184434.3a29c0f9.kamezawa.hiroyu@jp.fujitsu.com> <20100805185713.4d09339e.kamezawa.hiroyu@jp.fujitsu.com> <20100806131053.411dce6d.kamezawa.hiroyu@jp.fujitsu.com> From: Greg Thelen Date: Thu, 5 Aug 2010 21:37:29 -0700 Message-ID: Subject: Re: [PATCH 1/4 -mm][memcg] quick ID lookup in memcg To: KAMEZAWA Hiroyuki Cc: linux-mm@kvack.org, "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , vgoyal@redhat.com, m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5604 Lines: 153 On Thu, Aug 5, 2010 at 9:10 PM, KAMEZAWA Hiroyuki wrote: > On Thu, 05 Aug 2010 21:12:50 -0700 > Greg Thelen wrote: > >> KAMEZAWA Hiroyuki writes: >> >> > From: KAMEZAWA Hiroyuki >> > >> > Now, memory cgroup has an ID per cgroup and make use of it at >> > ?- hierarchy walk, >> > ?- swap recording. >> > >> > This patch is for making more use of it. The final purpose is >> > to replace page_cgroup->mem_cgroup's pointer to an unsigned short. >> > >> > This patch caches a pointer of memcg in an array. By this, we >> > don't have to call css_lookup() which requires radix-hash walk. >> > This saves some amount of memory footprint at lookup memcg via id. >> > >> > Changelog: 20100804 >> > ?- fixed description in init/Kconfig >> > >> > Changelog: 20100730 >> > ?- fixed rcu_read_unlock() placement. >> > >> > Signed-off-by: KAMEZAWA Hiroyuki >> > --- >> > ?init/Kconfig ? ?| ? 10 ++++++++++ >> > ?mm/memcontrol.c | ? 48 ++++++++++++++++++++++++++++++++++-------------- >> > ?2 files changed, 44 insertions(+), 14 deletions(-) >> > >> > Index: mmotm-0727/mm/memcontrol.c >> > =================================================================== >> > --- mmotm-0727.orig/mm/memcontrol.c >> > +++ mmotm-0727/mm/memcontrol.c >> > @@ -292,6 +292,30 @@ static bool move_file(void) >> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? &mc.to->move_charge_at_immigrate); >> > ?} >> > >> > +/* 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; >> > + >> > +static struct mem_cgroup *id_to_memcg(unsigned short id) >> > +{ >> > + ? /* >> > + ? ?* This array is set to NULL when mem_cgroup is freed. >> > + ? ?* IOW, there are no more references && rcu_synchronized(). >> > + ? ?* This lookup-caching is safe. >> > + ? ?*/ >> > + ? if (unlikely(!mem_cgroups[id])) { >> > + ? ? ? ? ? struct cgroup_subsys_state *css; >> > + >> > + ? ? ? ? ? rcu_read_lock(); >> > + ? ? ? ? ? css = css_lookup(&mem_cgroup_subsys, id); >> > + ? ? ? ? ? rcu_read_unlock(); >> > + ? ? ? ? ? if (!css) >> > + ? ? ? ? ? ? ? ? ? return NULL; >> > + ? ? ? ? ? mem_cgroups[id] = container_of(css, struct mem_cgroup, css); >> > + ? } >> > + ? return mem_cgroups[id]; >> > +} >> >> I am worried that id may be larger than CONFIG_MEM_CGROUP_MAX_GROUPS and >> cause an illegal array index. ?I see that >> mem_cgroup_uncharge_swapcache() uses css_id() to compute 'id'. >> mem_cgroup_num ensures that there are never more than >> CONFIG_MEM_CGROUP_MAX_GROUPS memcg active. ?But do we have guarantee >> that the that all of the css_id of each active memcg are less than >> NR_MEMCG_GROUPS? >> > Yes. kernel/cgroup.c's ID assign routine use the smallest number, always. > > > >> > ?/* >> > ? * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft >> > ? * limit reclaim to prevent infinite loops, if they ever occur. >> > @@ -1824,18 +1848,7 @@ static void mem_cgroup_cancel_charge(str >> > ? * it's concern. (dropping refcnt from swap can be called against removed >> > ? * memcg.) >> > ? */ >> > -static struct mem_cgroup *mem_cgroup_lookup(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) >> > - ? ? ? ? ? return NULL; >> > - ? return container_of(css, struct mem_cgroup, css); >> > -} >> > >> > ?struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page) >> > ?{ >> > @@ -1856,7 +1869,7 @@ struct mem_cgroup *try_get_mem_cgroup_fr >> > ? ? ? ? ? ? ent.val = page_private(page); >> > ? ? ? ? ? ? id = lookup_swap_cgroup(ent); >> > ? ? ? ? ? ? rcu_read_lock(); >> > - ? ? ? ? ? mem = mem_cgroup_lookup(id); >> > + ? ? ? ? ? mem = id_to_memcg(id); >> > ? ? ? ? ? ? if (mem && !css_tryget(&mem->css)) >> > ? ? ? ? ? ? ? ? ? ? mem = NULL; >> > ? ? ? ? ? ? rcu_read_unlock(); >> > @@ -2208,7 +2221,7 @@ __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 >> > @@ -2472,7 +2485,7 @@ 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. >> > @@ -3988,6 +4001,9 @@ static struct mem_cgroup *mem_cgroup_all >> > ? ? struct mem_cgroup *mem; >> > ? ? int size = sizeof(struct mem_cgroup); >> > >> > + ? if (atomic_read(&mem_cgroup_num) == NR_MEMCG_GROUPS) >> > + ? ? ? ? ? return NULL; >> > + >> >> I think that multiple tasks to be simultaneously running >> mem_cgroup_create(). ?Therefore more than NR_MEMCG_GROUPS memcg may be >> created. >> > > No. cgroup_mutex() is held. > > Thanks, > -Kame > > I see that now. Thank you clarification. I am doing some testing on the patches now. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/