From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932192AbXDFTge (ORCPT ); Fri, 6 Apr 2007 15:36:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932173AbXDFTge (ORCPT ); Fri, 6 Apr 2007 15:36:34 -0400 Received: from mail.screens.ru ([213.234.233.54]:45684 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751999AbXDFTgd (ORCPT ); Fri, 6 Apr 2007 15:36:33 -0400 Date: Fri, 6 Apr 2007 23:36:21 +0400 From: Oleg Nesterov To: Linus Torvalds Cc: "Eric W. Biederman" , Robin Holt , Chris Snook , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: init's children list is long and slows reaping children. Message-ID: <20070406193621.GA96@tv-sign.ru> References: <20070406084250.GA179@tv-sign.ru> <20070406094413.GA673@tv-sign.ru> <20070406154750.GA541@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 04/06, Linus Torvalds wrote: > > On Fri, 6 Apr 2007, Oleg Nesterov wrote: > > > > Oops. I misread stop_machine(), it does kernel_thread(), not kthread_create(). > > So "stopmachine" threads are all re-parented to init when the caller exits. > > I think it makes sense to set ->exit_state = -1 in stopmachine(), regadless > > of any other changes. > > I agree that "->exit_state = -1" makes sense, but I disagree in that I > don't think it *matters*. > > Most of the problematic kernel threads are long-running (as in "never > exit"). Things like eventd, khelper, migration-threads etc will have init > as their parent and never actually exit, so their ->exit_state doesn't > matter. What matters is that they are on the children list, so when you > have 1024 CPU's, and init has many thousand of these per-cpu threads as > its children, then the *user* threads (that do exit) will cause problems! > > I'd almost prefer to just not add kernel threads to any parent process > list *at*all*. Yes sure, I didn't argue with that. However, "->exit_state = -1" does matter, we can't detach process unless we make it auto-reap. Perhaps, --- t/kernel/exit.c~ 2007-04-06 23:31:31.000000000 +0400 +++ t/kernel/exit.c 2007-04-06 23:31:57.000000000 +0400 @@ -275,10 +275,7 @@ static void reparent_to_init(void) remove_parent(current); current->parent = child_reaper(current); current->real_parent = child_reaper(current); - add_parent(current); - - /* Set the exit signal to SIGCHLD so we signal init on exit */ - current->exit_signal = SIGCHLD; + current->exit_signal = -1; if (!has_rt_policy(current) && (task_nice(current) < 0)) set_user_nice(current, 0); is enough. init is still our parent (make ps happy), but it can't see us, we are not on ->children list. Off course, we also need to add preparent_to_init() to kthread() and (say) stopmachine(). Or we can create kernel_thread_detached() and modify callers to use it. Oleg.