From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755737Ab0DFNFd (ORCPT ); Tue, 6 Apr 2010 09:05:33 -0400 Received: from qw-out-2122.google.com ([74.125.92.27]:15912 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754567Ab0DFNF0 (ORCPT ); Tue, 6 Apr 2010 09:05:26 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=caTPadXHnETzNYVHtDyodlaklPuYsUnpVMw9DkPWiQr8uB3GPPV68yUud0za44a22m v0/AgfB2GN0Z75f0dH3kD9nor0AoKhaa13n0DhHCu+RVRGDFqAeK9cLaePvPnvs1gCns BO0Z1kuTHKuZCS/yuwbwxczEozeD7RugTaX0g= Date: Tue, 6 Apr 2010 21:05:19 +0800 From: anfei To: Oleg Nesterov Cc: David Rientjes , Andrew Morton , KOSAKI Motohiro , nishimura@mxp.nes.nec.co.jp, KAMEZAWA Hiroyuki , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm 2/4] oom: select_bad_process: PF_EXITING check should take ->mm into account Message-ID: <20100406130518.GB3965@desktop> References: <20100331175836.GA11635@redhat.com> <20100331204718.GD11635@redhat.com> <20100401135927.GA12460@redhat.com> <20100402111406.GA4432@redhat.com> <20100402183057.GA31723@redhat.com> <20100402183216.GC31723@redhat.com> <20100406114235.GA3965@desktop> <20100406121811.GA6802@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100406121811.GA6802@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 06, 2010 at 02:18:11PM +0200, Oleg Nesterov wrote: > On 04/06, anfei wrote: > > > > On Fri, Apr 02, 2010 at 08:32:16PM +0200, Oleg Nesterov wrote: > > > select_bad_process() checks PF_EXITING to detect the task which > > > is going to release its memory, but the logic is very wrong. > > > > > > - a single process P with the dead group leader disables > > > select_bad_process() completely, it will always return > > > ERR_PTR() while P can live forever > > > > > > - if the PF_EXITING task has already released its ->mm > > > it doesn't make sense to expect it is goiing to free > > > more memory (except task_struct/etc) > > > > > > Change the code to ignore the PF_EXITING tasks without ->mm. > > > > > > Signed-off-by: Oleg Nesterov > > > --- > > > > > > mm/oom_kill.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > --- MM/mm/oom_kill.c~2_FIX_PF_EXITING 2010-04-02 18:51:05.000000000 +0200 > > > +++ MM/mm/oom_kill.c 2010-04-02 18:58:37.000000000 +0200 > > > @@ -322,7 +322,7 @@ static struct task_struct *select_bad_pr > > > * the process of exiting and releasing its resources. > > > * Otherwise we could get an easy OOM deadlock. > > > */ > > > - if (p->flags & PF_EXITING) { > > > + if ((p->flags & PF_EXITING) && p->mm) { > > > > Even this check is satisfied, it still can't say p is a good victim or > > it will release memory automatically if multi threaded, as the exiting > > of p doesn't mean the other threads are going to exit, so the ->mm won't > > be released. > > Yes, completely agreed. > > Unfortunately I forgot to copy this into the changelog, but when I > discussed this change I mentioned "still not perfect, but much better". > > I do not really know what is the "right" solution. Even if we fix this > check for mt case, we also have CLONE_VM tasks. > What about checking mm->mm_users too? If there are any other users, just let badness judge. CLONE_VM tasks but not mt seem rare, and badness doesn't consider it too. > So, this patch just tries to improve things, to avoid the easy-to-trigger > false positives. > Agreed. Thanks, Anfei. > Oleg. >