From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753183AbaJTTqm (ORCPT ); Mon, 20 Oct 2014 15:46:42 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:42423 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752517AbaJTTqk (ORCPT ); Mon, 20 Oct 2014 15:46:40 -0400 Date: Mon, 20 Oct 2014 15:46:34 -0400 From: Johannes Weiner To: Michal Hocko Cc: Andrew Morton , Hugh Dickins , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch] mm: memcontrol: update mem_cgroup_page_lruvec() documentation Message-ID: <20141020194634.GA12120@phnom.home.cmpxchg.org> References: <1413732616-15962-1-git-send-email-hannes@cmpxchg.org> <20141020191256.GD505@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141020191256.GD505@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 20, 2014 at 09:12:56PM +0200, Michal Hocko wrote: > On Sun 19-10-14 11:30:16, Johannes Weiner wrote: > > 7512102cf64d ("memcg: fix GPF when cgroup removal races with last > > exit") added a pc->mem_cgroup reset into mem_cgroup_page_lruvec() to > > prevent a crash where an anon page gets uncharged on unmap, the memcg > > is released, and then the final LRU isolation on free dereferences the > > stale pc->mem_cgroup pointer. > > > > But since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API"), pages > > are only uncharged AFTER that final LRU isolation, which guarantees > > the memcg's lifetime until then. pc->mem_cgroup now only needs to be > > reset for swapcache readahead pages. > > Do we want VM_BUG_ON_PAGE(!PageSwapCache, page) into the fixup path? While that is what we expect as of right now, it's not really a requirement for this function. Should somebody later add other page types they might trigger this assertion and scratch their head about it and wonder if they're missing some non-obvious dependency. > > Update the comment and callsite requirements accordingly. > > > > Signed-off-by: Johannes Weiner > > Acked-by: Michal Hocko Thanks!