From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id E5B4A6B01F8 for ; Tue, 6 Apr 2010 09:05:27 -0400 (EDT) Date: Tue, 6 Apr 2010 21:05:19 +0800 From: anfei 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> Sender: owner-linux-mm@kvack.org 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 List-ID: 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. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org