From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757031AbbIUPfz (ORCPT ); Mon, 21 Sep 2015 11:35:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45088 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756425AbbIUPfy (ORCPT ); Mon, 21 Sep 2015 11:35:54 -0400 Date: Mon, 21 Sep 2015 17:32:52 +0200 From: Oleg Nesterov To: Michal Hocko Cc: Linus Torvalds , Kyle Walker , Christoph Lameter , Andrew Morton , David Rientjes , Johannes Weiner , Vladimir Davydov , linux-mm , Linux Kernel Mailing List , Stanislav Kozina , Tetsuo Handa Subject: Re: can't oom-kill zap the victim's memory? Message-ID: <20150921153252.GA21988@redhat.com> References: <1442512783-14719-1-git-send-email-kwalker@redhat.com> <20150919150316.GB31952@redhat.com> <20150920125642.GA2104@redhat.com> <20150921134414.GA15974@redhat.com> <20150921142423.GC19811@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150921142423.GC19811@dhcp22.suse.cz> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/21, Michal Hocko wrote: > > On Mon 21-09-15 15:44:14, Oleg Nesterov wrote: > [...] > > So yes, in general oom_kill_process() can't call oom_unmap_func() directly. > > That is why the patch uses queue_work(oom_unmap_func). The workqueue thread > > takes mmap_sem and frees the memory allocated by user space. > > OK, this might have been a bit confusing. I didn't mean you cannot use > mmap_sem directly from the workqueue context. You _can_ AFAICS. But I've > mentioned that you _shouldn't_ use workqueue context in the first place > because all the workers might be blocked on locks and new workers cannot > be created due to memory pressure. Yes, yes, and I already tried to comment this part. We probably need a dedicated kernel thread, but I still think (although I am not sure) that initial change can use workueue. In the likely case system_unbound_wq pool should have an idle thread, if not - OK, this change won't help in this case. This is minor. > So I think we probably need to do this in the OOM killer context (with > try_lock) Yes we should try to do this in the OOM killer context, and in this case (of course) we need trylock. Let me quote my previous email: And we want to avoid using workqueues when the caller can do this directly. And in this case we certainly need trylock. But this needs some refactoring: we do not want to do this under oom_lock, otoh it makes sense to do this from mark_oom_victim() if current && killed, and a lot more details. and probably this is another reason why do we need MMF_MEMDIE. But again, I think the initial change should be simple. Oleg.