From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753428Ab1K1JRP (ORCPT ); Mon, 28 Nov 2011 04:17:15 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:60336 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750865Ab1K1JRO (ORCPT ); Mon, 28 Nov 2011 04:17:14 -0500 Date: Mon, 28 Nov 2011 10:17:03 +0100 From: Johannes Weiner To: Balbir Singh Cc: Andrew Morton , KAMEZAWA Hiroyuki , Michal Hocko , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [patch 4/8] mm: memcg: lookup_page_cgroup (almost) never returns NULL Message-ID: <20111128091703.GB9356@cmpxchg.org> References: <1322062951-1756-1-git-send-email-hannes@cmpxchg.org> <1322062951-1756-5-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 28, 2011 at 12:33:31PM +0530, Balbir Singh wrote: > On Wed, Nov 23, 2011 at 9:12 PM, Johannes Weiner wrote: > > From: Johannes Weiner > > > > Pages have their corresponding page_cgroup descriptors set up before > > they are used in userspace, and thus managed by a memory cgroup. > > > > The only time where lookup_page_cgroup() can return NULL is in the > > page sanity checking code that executes while feeding pages into the > > page allocator for the first time. > > > > This is a legacy check from the days when we allocated PC during fault > time on demand. It might make sense to assert on !pc in DEBUG_VM mode > at some point in the future I don't think a BUG_ON bears more information than a null-pointer dereference.