Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758363Ab1FJXy4 (ORCPT ); Fri, 10 Jun 2011 19:54:56 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:37669 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751894Ab1FJXyz (ORCPT ); Fri, 10 Jun 2011 19:54:55 -0400 Date: Sat, 11 Jun 2011 01:54:42 +0200 From: Johannes Weiner To: Hugh Dickins Cc: KAMEZAWA Hiroyuki , Andrea Arcangeli , Ying Han , Dave Jones , Linux Kernel , "linux-mm@kvack.org" , Oleg Nesterov , "akpm@linux-foundation.org" Subject: Re: [PATCH] [BUGFIX] update mm->owner even if no next owner. Message-ID: <20110610235442.GA21413@cmpxchg.org> References: <20110609212956.GA2319@redhat.com> <20110610091355.2ce38798.kamezawa.hiroyu@jp.fujitsu.com> <20110610113311.409bb423.kamezawa.hiroyu@jp.fujitsu.com> <20110610121949.622e4629.kamezawa.hiroyu@jp.fujitsu.com> <20110610125551.385ea7ed.kamezawa.hiroyu@jp.fujitsu.com> <20110610133021.2eaaf0da.kamezawa.hiroyu@jp.fujitsu.com> 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 Content-Length: 1500 Lines: 40 On Fri, Jun 10, 2011 at 02:49:35PM -0700, Hugh Dickins wrote: > On Fri, 10 Jun 2011, KAMEZAWA Hiroyuki wrote: > > > > I think this can be a fix. > > Sorry, I think not: I've not digested your rationale, > but three things stand out: > > 1. Why has this only just started happening? I may not have run that > test on 3.0-rc1, but surely I ran it for hours with 2.6.39; > maybe not with khugepaged, but certainly with ksmd. > > 2. Your hunk below: > > - if (!mm_need_new_owner(mm, p)) > > + if (!mm_need_new_owner(mm, p)) { > > + rcu_assign_pointer(mm->owner, NULL); > is now setting mm->owner to NULL at times when we were sure it did not > need updating before (task is not the owner): you're damaging mm->owner. > > 3. There's a patch from Andrea in 3.0-rc1 which looks very likely to be > relevant, 692e0b35427a "mm: thp: optimize memcg charge in khugepaged". > I'll try reproducing without that tonight (I crashed in 20 minutes > this morning, so it's not too hard). It looks likely. This change moved the memcg charge out of the mmap_sem read section, which kept the last task of the mm from exiting: do_exit exit_mm mmput khugepaged_exit down_write(&mm->mmap_sem); up_write(&mm->mmap_sem); -- 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/