Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751992AbaDQUXJ (ORCPT ); Thu, 17 Apr 2014 16:23:09 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:33371 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751668AbaDQUWp (ORCPT ); Thu, 17 Apr 2014 16:22:45 -0400 Date: Thu, 17 Apr 2014 21:22:37 +0100 From: Al Viro To: "Eric W. Biederman" Cc: Linus Torvalds , "Serge E. Hallyn" , Linux-Fsdevel , Kernel Mailing List , Andy Lutomirski , Rob Landley , Miklos Szeredi , Christoph Hellwig , Karel Zak , "J. Bruce Fields" , Fengguang Wu , tytso@mit.edu Subject: Re: [GIT PULL] Detaching mounts on unlink for 3.15 Message-ID: <20140417202237.GA18016@ZenIV.linux.org.uk> References: <87fvlm860e.fsf_-_@x220.int.ebiederm.org> <20140409232423.GB18016@ZenIV.linux.org.uk> <87lhva5h4k.fsf@x220.int.ebiederm.org> <20140413053956.GM18016@ZenIV.linux.org.uk> <87zjjp3e7w.fsf@x220.int.ebiederm.org> <87ppkl1xb7.fsf@x220.int.ebiederm.org> <20140413215242.GP18016@ZenIV.linux.org.uk> <87y4z8uzqw.fsf_-_@x220.int.ebiederm.org> <87ppkhc4pp.fsf@x220.int.ebiederm.org> <87ha5r3emw.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ha5r3emw.fsf_-_@x220.int.ebiederm.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Have you tried to profile something like umount -l on a large mount tree? You variant causes a shitstorm of schedule work switch to workqueue do actual fs shutdown wake umount(8) up get through wait_for_completion() for every bleeding vfsmount in there. And no, it's *not* guaranteed to be dominated by fs shutdown time. Here's the case where it definitely won't be: mkdir /tmp/a mount --rbind / /tmp/a umount -l /tmp/a All vfsmounts involved are killed off with no fs shutdown. And that's *not* a rare case - exit of the last process in namespace is very likely to look that way too. That's far too heavy. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/