From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753248AbbITO67 (ORCPT ); Sun, 20 Sep 2015 10:58:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37662 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752342AbbITO65 (ORCPT ); Sun, 20 Sep 2015 10:58:57 -0400 Date: Sun, 20 Sep 2015 16:55:57 +0200 From: Oleg Nesterov To: Tetsuo Handa Cc: kwalker@redhat.com, cl@linux.com, torvalds@linux-foundation.org, mhocko@kernel.org, akpm@linux-foundation.org, rientjes@google.com, hannes@cmpxchg.org, vdavydov@parallels.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, skozina@redhat.com Subject: Re: can't oom-kill zap the victim's memory? Message-ID: <20150920145557.GA10200@redhat.com> References: <1442512783-14719-1-git-send-email-kwalker@redhat.com> <20150919150316.GB31952@redhat.com> <201509202350.DDG21892.FFStOLHOQOFMVJ@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201509202350.DDG21892.FFStOLHOQOFMVJ@I-love.SAKURA.ne.jp> 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 09/20, Tetsuo Handa wrote: > > Oleg Nesterov wrote: > > On 09/17, Kyle Walker wrote: > > > > > > Currently, the oom killer will attempt to kill a process that is in > > > TASK_UNINTERRUPTIBLE state. For tasks in this state for an exceptional > > > period of time, such as processes writing to a frozen filesystem during > > > a lengthy backup operation, this can result in a deadlock condition as > > > related processes memory access will stall within the page fault > > > handler. > > > > And there are other potential reasons for deadlock. > > > > Stupid idea. Can't we help the memory hog to free its memory? This is > > orthogonal to other improvements we can do. > > So, we are trying to release memory without waiting for arriving at > exit_mm() from do_exit(), right? If it works, it will be a simple and > small change that will be easy to backport. > > The idea is that since fatal_signal_pending() tasks no longer return to > user space, we can release memory allocated for use by user space, right? Yes. > Then, I think that this approach can be applied to not only OOM-kill case > but also regular kill(pid, SIGKILL) case (i.e. kick from signal_wake_up(1) > or somewhere?). I don't think so... but we might want to do this if (say) we are not going to kill someone else because fatal_signal_pending(current). > A dedicated kernel thread (not limited to OOM-kill purpose) > scans for fatal_signal_pending() tasks and release that task's memory. Perhaps a dedicated kernel thread makes sense (see other emails), but I don't think it should scan the killed threads. oom-kill should kict it. Anyway, let me repeat there are a lot of details we might want to discuss. But the initial changes should be simple as possible, imo. Oleg.