From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id C8B956B0353 for ; Mon, 23 Aug 2010 22:01:13 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o7O217AZ014345 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 24 Aug 2010 11:01:08 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 896D345DE51 for ; Tue, 24 Aug 2010 11:01:07 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 4BC3B45DD77 for ; Tue, 24 Aug 2010 11:01:07 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 365A01DB803B for ; Tue, 24 Aug 2010 11:01:07 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id E91F71DB8038 for ; Tue, 24 Aug 2010 11:01:06 +0900 (JST) Date: Tue, 24 Aug 2010 10:54:05 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] memcg: use ID in page_cgroup Message-Id: <20100824105405.abf226e6.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20100824101425.2dc25773.nishimura@mxp.nes.nec.co.jp> References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820190132.43684862.kamezawa.hiroyu@jp.fujitsu.com> <20100823143237.b7822ffc.nishimura@mxp.nes.nec.co.jp> <20100824085243.8dd3c8de.kamezawa.hiroyu@jp.fujitsu.com> <20100824101425.2dc25773.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Daisuke Nishimura 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 List-ID: On Tue, 24 Aug 2010 10:14:25 +0900 Daisuke Nishimura wrote: > > > > @@ -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(). > > > > > > > Why ?? > > > Just to make sure that the root css has id==1. mem_cgroup_is_rootid() make > use of the fact. > I'm sorry if I miss something. > Hmm. The function allocating ID does 4530 static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth) 4531 { == 4546 spin_lock(&ss->id_lock); 4547 /* Don't use 0. allocates an ID of 1-65535 */ 4548 error = idr_get_new_above(&ss->idr, newid, 1, &myid); 4549 spin_unlock(&ss->id_lock); == and allocates ID above "1", always. Adding BUG_ON(newid->id != 1) will mean that we doubt the bitmap function and consider possibility that new->id == 0. But, we're 100% sure that it never happens. I don't think adding a comment is a right thing to do. Thanks, -Kame -- 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