From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 705B26B0092 for ; Mon, 24 Jan 2011 05:45:19 -0500 (EST) Date: Mon, 24 Jan 2011 11:45:10 +0100 From: Johannes Weiner Subject: Re: [PATCH 1/7] memcg : comment, style fixes for recent patch of move_parent Message-ID: <20110124104510.GW2232@cmpxchg.org> References: <20110121153431.191134dd.kamezawa.hiroyu@jp.fujitsu.com> <20110121153726.54f4a159.kamezawa.hiroyu@jp.fujitsu.com> <20110124101402.GT2232@cmpxchg.org> <20110124191535.514ef2d9.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110124191535.514ef2d9.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" , "balbir@linux.vnet.ibm.com" , "akpm@linux-foundation.org" List-ID: On Mon, Jan 24, 2011 at 07:15:35PM +0900, KAMEZAWA Hiroyuki wrote: > On Mon, 24 Jan 2011 11:14:02 +0100 > Johannes Weiner wrote: > > > On Fri, Jan 21, 2011 at 03:37:26PM +0900, KAMEZAWA Hiroyuki wrote: > > > From: KAMEZAWA Hiroyuki > > > > > > A fix for 987eba66e0e6aa654d60881a14731a353ee0acb4 > > > > > > A clean up for mem_cgroup_move_parent(). > > > - remove unnecessary initialization of local variable. > > > - rename charge_size -> page_size > > > - remove unnecessary (wrong) comment. > > > > > > Signed-off-by: KAMEZAWA Hiroyuki > > > --- > > > mm/memcontrol.c | 17 +++++++++-------- > > > 1 file changed, 9 insertions(+), 8 deletions(-) > > > > > > Index: mmotm-0107/mm/memcontrol.c > > > =================================================================== > > > --- mmotm-0107.orig/mm/memcontrol.c > > > +++ mmotm-0107/mm/memcontrol.c > > > @@ -2265,7 +2265,7 @@ static int mem_cgroup_move_parent(struct > > > struct cgroup *cg = child->css.cgroup; > > > struct cgroup *pcg = cg->parent; > > > struct mem_cgroup *parent; > > > - int charge = PAGE_SIZE; > > > + int page_size; > > > unsigned long flags; > > > int ret; > > > > > > @@ -2278,22 +2278,23 @@ static int mem_cgroup_move_parent(struct > > > goto out; > > > if (isolate_lru_page(page)) > > > goto put; > > > - /* The page is isolated from LRU and we have no race with splitting */ > > > - charge = PAGE_SIZE << compound_order(page); > > > + > > > + page_size = PAGE_SIZE << compound_order(page); > > > > Okay, so you remove the wrong comment, but that does not make the code > > right. What protects compound_order from reading garbage because the > > page is currently splitting? > > > > == > static int mem_cgroup_move_account(struct page_cgroup *pc, > struct mem_cgroup *from, struct mem_cgroup *to, > bool uncharge, int charge_size) > { > int ret = -EINVAL; > unsigned long flags; > > if ((charge_size > PAGE_SIZE) && !PageTransHuge(pc->page)) > return -EBUSY; > == > > This is called under compound_lock(). Then, if someone breaks THP, > -EBUSY and retry. This charge_size contains exactly the garbage you just read from an unprotected compound_order(). It could be anything if the page is split concurrently. -- 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