From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id D2F7A6B0203 for ; Mon, 23 Aug 2010 01:52:41 -0400 (EDT) Date: Mon, 23 Aug 2010 14:32:37 +0900 From: Daisuke Nishimura Subject: Re: [PATCH] memcg: use ID in page_cgroup Message-Id: <20100823143237.b7822ffc.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20100820190132.43684862.kamezawa.hiroyu@jp.fujitsu.com> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820190132.43684862.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: On Fri, 20 Aug 2010 19:01:32 +0900 KAMEZAWA Hiroyuki wrote: > > I have an idea to remove page_cgroup->page pointer, 8bytes reduction per page. > But it will be after this work. Another off topic. I think we can reduce the size of mem_cgroup by packing some boolean members into one "unsinged long flags". > @@ -300,12 +300,13 @@ 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; > > -/* Must be called under rcu_read_lock */ > -static struct mem_cgroup *id_to_memcg(unsigned short id) > +/* Must be called under rcu_read_lock, set safe==true if under lock */ Do you mean, "Set safe==true if we can ensure by some locks that the id can be safely dereferenced without rcu_read_lock", right ? > +static struct mem_cgroup *id_to_memcg(unsigned short id, bool safe) > { > struct mem_cgroup *ret; > /* see mem_cgroup_free() */ > - ret = rcu_dereference_check(mem_cgroups[id], rch_read_lock_held()); > + ret = rcu_dereference_check(mem_cgroups[id], > + rch_read_lock_held() || safe); > if (likely(ret && ret->valid)) > return ret; > return NULL; (snip) > @@ -723,6 +729,11 @@ static inline bool mem_cgroup_is_root(st > return (mem == root_mem_cgroup); > } > > +static inline bool mem_cgroup_is_rootid(unsigned short id) > +{ > + return (id == 1); > +} > + It might be better to add BUG_ON(newid->id != 1) in cgroup.c::cgroup_init_idr(). Thanks, 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