From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757070AbdESUpI (ORCPT ); Fri, 19 May 2017 16:45:08 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:36546 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756793AbdESUpG (ORCPT ); Fri, 19 May 2017 16:45:06 -0400 Date: Fri, 19 May 2017 13:44:57 -0700 From: Dmitry Torokhov To: "Luis R. Rodriguez" Cc: shuah@kernel.org, jeyu@redhat.com, rusty@rustcorp.com.au, ebiederm@xmission.com, acme@redhat.com, corbet@lwn.net, martin.wilck@suse.com, mmarek@suse.com, pmladek@suse.com, hare@suse.com, rwright@hpe.com, jeffm@suse.com, DSterba@suse.com, fdmanana@suse.com, neilb@suse.com, linux@roeck-us.net, rgoldwyn@suse.com, subashab@codeaurora.org, xypron.glpk@gmx.de, keescook@chromium.org, atomlin@redhat.com, mbenes@suse.cz, paulmck@linux.vnet.ibm.com, dan.j.williams@intel.com, jpoimboe@redhat.com, davem@davemloft.net, mingo@redhat.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, gregkh@linuxfoundation.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/6] kmod: add dynamic max concurrent thread count Message-ID: <20170519204457.GC19281@dtor-ws> References: <20170519032444.18416-1-mcgrof@kernel.org> <20170519032444.18416-2-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170519032444.18416-2-mcgrof@kernel.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 On Thu, May 18, 2017 at 08:24:39PM -0700, Luis R. Rodriguez wrote: > We currently statically limit the number of modprobe threads which > we allow to run concurrently to 50. As per Keith Owens, this was a > completely arbitrary value, and it was set in the 2.3.38 days [0] > over 16 years ago in year 2000. > > Although we haven't yet hit our lower limits, experimentation [1] > shows that when and if we hit this limit in the worst case, will be > fatal -- consider get_fs_type() failures upon mount on a system which > has many partitions, some of which might even be with the same > filesystem. Its best to be prudent and increase and set this > value to something more sensible which ensures we're far from hitting > the limit and also allows default build/user run time override. > > The worst case is fatal given that once a module fails to load there > is a period of time during which subsequent request for the same module > will fail, so in the case of partitions its not just one request that > could fail, but whole series of partitions. This later issue of a > module request failure domino effect can be addressed later, but > increasing the limit to something more meaninful should at least give us > enough cushion to avoid this for a while. > > Set this value up with a bit more meaninful modern limits: > > Bump this up to 64 max for small systems (CONFIG_BASE_SMALL) > Bump this up to 128 max for larger systems (!CONFIG_BASE_SMALL) > > Also allow the default max limit to be further fine tuned at compile > time and at initialization at run time at boot up using the kernel > parameter: max_modprobes. > > [0] https://git.kernel.org/cgit/linux/kernel/git/history/history.git/commit/?id=ab1c4ec7410f6ec64e1511d1a7d850fc99c09b44 > [1] https://github.com/mcgrof/test_request_module If we actually run into this issue, instead of slamming the system with bazillion concurrent requests, can we wait for the other modprobes to finish and then continue? Thanks. -- Dmitry