From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 937426B0092 for ; Wed, 19 Jan 2011 07:10:49 -0500 (EST) Date: Wed, 19 Jan 2011 13:10:43 +0100 From: Johannes Weiner Subject: Re: [PATCH 2/4] memcg: fix USED bit handling at uncharge in THP Message-ID: <20110119121043.GB2232@cmpxchg.org> References: <20110118113528.fd24928f.kamezawa.hiroyu@jp.fujitsu.com> <20110118114049.5ffdf5da.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110118114049.5ffdf5da.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "nishimura@mxp.nes.nec.co.jp" , "balbir@linux.vnet.ibm.com" List-ID: Hello KAMEZAWA-san, On Tue, Jan 18, 2011 at 11:40:49AM +0900, KAMEZAWA Hiroyuki wrote: > +void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail) > +{ > + struct page_cgroup *head_pc = lookup_page_cgroup(head); > + struct page_cgroup *tail_pc = lookup_page_cgroup(tail); > + unsigned long flags; > + > + /* > + * We have no races witch charge/uncharge but will have races with > + * page state accounting. > + */ > + move_lock_page_cgroup(head_pc, &flags); > + > + tail_pc->mem_cgroup = head_pc->mem_cgroup; > + smp_wmb(); /* see __commit_charge() */ I thought the barriers were needed because charging does not hold the lru lock. But here we do, and all the 'lockless' read-sides do so as well. Am I missing something or can this barrier be removed? Hannes -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org