From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754600Ab1HRVzX (ORCPT ); Thu, 18 Aug 2011 17:55:23 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:44467 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754006Ab1HRVzT (ORCPT ); Thu, 18 Aug 2011 17:55:19 -0400 Subject: Re: + prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision .patch added to -mm tree From: Kay Sievers To: Linus Torvalds Cc: Oleg Nesterov , Lennart Poettering , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-man@vger.kernel.org, roland@hack.frob.com Date: Thu, 18 Aug 2011 23:55:15 +0200 In-Reply-To: References: <201108162011.p7GKBcY0023134@imap1.linux-foundation.org> <20110817115543.GA8745@redhat.com> <20110817134516.GA14136@redhat.com> <20110818124353.GA2839@tango.0pointer.de> <20110818142508.GA30959@redhat.com> <1313691091.1107.9.camel@mop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.1.4 (3.1.4-1.fc16) Content-Transfer-Encoding: 7bit Message-ID: <1313704516.15082.5.camel@mop> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 18, 2011 at 23:23, Linus Torvalds wrote: > On Thu, Aug 18, 2011 at 11:11 AM, Kay Sievers wrote: >> >> How about this? It: >> - uses task->real_parent to walk up the chain of parents. > > If I read this right, it does that for all the normal cases too. > Disgusting. Slowing down the *usual* UNIX case for your new made-up > case that nobody actually uses is not acceptable. Re-parenting is not a *usual* operation, usual exit()s have a parent and do not trigger that code. And in most cases of double-forking it is a one step, which is almost the same than it was before. Only if we skip multiple parents it will get the check, which is cheap anyway. > So NAK. We're not slowing down normal code for some new feature that > realistically will never be used by any normal applications. It will be used for all new service managers. UNIX is a pain if you want to watch your children regarding double-forking, if you are not init. And it will clean up the mess the desktop stuff is putting in 'ps afx'. Here is the before/after output: 253 ? Ss 0:00 /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation 294 ? Sl 0:00 /usr/libexec/polkit-1/polkitd 328 ? S 0:00 /usr/sbin/modem-manager 608 ? Sl 0:00 /usr/libexec/colord 658 ? Sl 0:00 /usr/libexec/upowerd 819 ? Sl 0:00 /usr/libexec/imsettings-daemon 916 ? Sl 0:00 /usr/libexec/udisks-daemon 917 ? S 0:00 \_ udisks-daemon: not polling any devices 294 ? Ss 0:00 /bin/dbus-daemon --system --address=systemd: --nofork --systemd-activation 426 ? Sl 0:00 \_ /usr/libexec/polkit-1/polkitd 449 ? S 0:00 \_ /usr/sbin/modem-manager 635 ? Sl 0:00 \_ /usr/libexec/colord 705 ? Sl 0:00 \_ /usr/libexec/upowerd 959 ? Sl 0:00 \_ /usr/libexec/udisks-daemon 960 ? S 0:00 | \_ udisks-daemon: not polling any devices 977 ? Sl 0:00 \_ /usr/libexec/packagekitd It's a pretty nice way for an admin too see what's going on on that box, even with good old 'ps'. It will also dramatically simplify the handling of started services from a service manager which double-fork for only historic reasons and make proper service supervision a nightmare if you are not PID 1. Upstart ptraces all started services to accomplish something similar. I doubt we want to go that road, but if you prefer ... :) If you want, we can make the forked processes inherit a flag if the 'subreaper' should be looked up at all. Then we have almost zero overhead if the feature isn't used. You think that's needed? Thanks, Kay