Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754110Ab1BDJ3k (ORCPT ); Fri, 4 Feb 2011 04:29:40 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:45583 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753748Ab1BDJ3h (ORCPT ); Fri, 4 Feb 2011 04:29:37 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Fri, 4 Feb 2011 18:23:21 +0900 From: KAMEZAWA Hiroyuki To: Johannes Weiner Cc: Andrew Morton , Daisuke Nishimura , Balbir Singh , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/5] memcg: no uncharged pages reach page_cgroup_zoneinfo Message-Id: <20110204182321.5ba58fdd.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20110204092650.GB2289@cmpxchg.org> References: <1296743166-9412-1-git-send-email-hannes@cmpxchg.org> <1296743166-9412-2-git-send-email-hannes@cmpxchg.org> <20110204090145.7f1918fc.kamezawa.hiroyu@jp.fujitsu.com> <20110204092650.GB2289@cmpxchg.org> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.1.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1820 Lines: 62 On Fri, 4 Feb 2011 10:26:50 +0100 Johannes Weiner wrote: > On Fri, Feb 04, 2011 at 09:01:45AM +0900, KAMEZAWA Hiroyuki wrote: > > On Thu, 3 Feb 2011 15:26:02 +0100 > > Johannes Weiner wrote: > > > > > All callsites check PCG_USED before passing pc->mem_cgroup, so the > > > latter is never NULL. > > > > > > Signed-off-by: Johannes Weiner > > > > Acked-by: KAMEZAWA Hiroyuki > > Thank you! > > > I want BUG_ON() here. > > I thought about it too at first. But look at the callsites, all but > one of them do not even expect this function to return NULL, so if > this condition had ever been true, we would have seen crashes in the > callsites. > Hmm ok. -Kame > The only caller that checks for NULL is > mem_cgroup_get_reclaim_stat_from_page() and I propose to remove that > as well; patch attached. > > Do you insist on the BUG_ON? > > --- > Subject: memcg: page_cgroup_zoneinfo never returns NULL > > For a page charged to a memcg, there is always valid memcg per-zone > info. > > Signed-off-by: Johannes Weiner > --- > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4a4483d..5f974b3 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1017,9 +1017,6 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page) > /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */ > smp_rmb(); > mz = page_cgroup_zoneinfo(pc->mem_cgroup, page); > - if (!mz) > - return NULL; > - > return &mz->reclaim_stat; > } > > -- 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/