From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964873AbcIWE0X (ORCPT ); Fri, 23 Sep 2016 00:26:23 -0400 Received: from out2-smtp.messagingengine.com ([66.111.4.26]:53316 "EHLO out2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751762AbcIWE0V (ORCPT ); Fri, 23 Sep 2016 00:26:21 -0400 X-Sasl-enc: eHLeHqC0JfzZa6e6AcHrrusPYf0KzdN+Yijz4ujjugmM 1474604779 Message-ID: <1474604774.3083.1.camel@themaw.net> Subject: Re: [PATCH 3/4] autofs - make mountpoint checks namespace aware From: Ian Kent To: "Eric W. Biederman" Cc: Mateusz Guzik , NeilBrown , Andrew Morton , autofs mailing list , Kernel Mailing List , Al Viro , linux-fsdevel , Omar Sandoval Date: Fri, 23 Sep 2016 12:26:14 +0800 In-Reply-To: <877fa39z1q.fsf@x220.int.ebiederm.org> References: <20160914061434.24714.490.stgit@pluto.themaw.net> <20160914061445.24714.68331.stgit@pluto.themaw.net> <20160917201000.omswgttgyzcu7jt6@mguzik> <1474248973.3204.14.camel@themaw.net> <87oa3iikgf.fsf@x220.int.ebiederm.org> <1474411462.22440.2.camel@themaw.net> <1474412413.22440.7.camel@themaw.net> <1474507987.12887.5.camel@themaw.net> <87k2e4c541.fsf@x220.int.ebiederm.org> <1474592141.3345.20.camel@themaw.net> <877fa39z1q.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 (3.16.5-3.fc22) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2016-09-22 at 20:37 -0500, Eric W. Biederman wrote: > Ian Kent writes: > > > On Thu, 2016-09-22 at 10:43 -0500, Eric W. Biederman wrote: > > > Ian Kent writes: > > > > > > > Eric, Mateusz, I appreciate your spending time on this and particularly > > > > pointing > > > > out my embarrassingly stupid is_local_mountpoint() usage mistake. > > > > > > > > Please accept my apology for the inconvenience. > > > > > > > > If all goes well (in testing) I'll have follow up patches to correct > > > > this > > > > fairly > > > > soon. > > > > > > Related question. Do you happen to know how many mounts per mount > > > namespace tend to be used? It looks like it is going to be wise to put > > > a configurable limit on that number. And I would like the default to be > > > something high enough most people don't care. I believe autofs is > > > likely where people tend to use the most mounts. Yes, I agree, I did want to try and avoid changing the parameters to ->d_mamange() but passing a struct path pointer might be better in the long run anyway. > > That's a good question. > > > > I've been thinking that maybe I should have used a lookup_mnt() type check > > as I > > originally started out to, for this reason, as the mnt_namespace list looks > > to > > be a linear list. > > > > But there can be a lot of mounts, and not only due to autofs, so maybe that > > should be considered anyway. > > There are two reasons for is_local_mountpoint being the way it is. > > a) For the cases where you don't have the parent mount. > b) For the cases where you want to stop things if something is mounted > on a dentry in the local mount namespace even if it isn't mounted > on that dentry at your current mount parent. (Something that was > important to not change the semantics of the single mount namespace case). > > Both of those cases to apply to unlink, rmdir, and rename. I don't think > either of those cases apply to what autofs is trying to do. Certainly > not the second. > > So if you have the parent mount I really think you want to be using some > variation of lookup_mnt(). The fact it is rcu safe may help with some > of those weird corner cases as well. > > > The number of mounts for direct mount maps is usually not very large because > > of > > the way they are implemented, large direct mount maps can have performance > > problems. There can be anywhere from a few (likely case a few hundred) to > > less > > than 10000, plus mounts that have been triggered and not yet expired. > > > > Indirect mounts have one autofs mount at the root plus the number of mounts > > that > > have been triggered and not yet expired. > > > > The number of autofs indirect map entries can range from a few to the common > > case of several thousand and in rare cases up to between 30000 and 50000. > > I've > > not heard of people with maps larger than 50000 entries. > > > > The larger the number of map entries the greater the possibility for a large > > number of active mounts so it's not hard to expect cases of a 1000 or > > somewhat > > more active mounts. > > Fair. So at least 1000. And there can be enough mounts that a limit of > 100,000 might be necessary to give head room for the existings configurations. > > Thank you. Now I just need to wrap my head around fs/namespace.c again > and see how bad a count like that will be to maintain. > > Eric >