From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752506AbdBGAWR (ORCPT ); Mon, 6 Feb 2017 19:22:17 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:36386 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752384AbdBGAWP (ORCPT ); Mon, 6 Feb 2017 19:22:15 -0500 Date: Mon, 6 Feb 2017 16:22:13 -0800 From: Andrew Morton To: Tejun Heo Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vladimir Davydov , linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Michal Hocko , kernel-team@fb.com Subject: Re: [PATCH] slub: make sysfs directories for memcg sub-caches optional Message-Id: <20170206162213.30f909b5ce4c681e2217fb4f@linux-foundation.org> In-Reply-To: <20170204145203.GB26958@mtj.duckdns.org> References: <20170204145203.GB26958@mtj.duckdns.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 4 Feb 2017 09:52:03 -0500 Tejun Heo wrote: > SLUB creates a per-cache directory under /sys/kernel/slab which hosts > a bunch of debug files. Usually, there aren't that many caches on a > system and this doesn't really matter; however, if memcg is in use, > each cache can have per-cgroup sub-caches. SLUB creates the same > directories for these sub-caches under /sys/kernel/slab/$CACHE/cgroup. > > Unfortunately, because there can be a lot of cgroups, active or > draining, the product of the numbers of caches, cgroups and files in > each directory can reach a very high number - hundreds of thousands is > commonplace. Millions and beyond aren't difficult to reach either. > > What's under /sys/kernel/slab is primarily for debugging and the > information and control on the a root cache already cover its > sub-caches. While having a separate directory for each sub-cache can > be helpful for development, it doesn't make much sense to pay this > amount of overhead by default. > > This patch introduces a boot parameter slub_memcg_sysfs which > determines whether to create sysfs directories for per-memcg > sub-caches. It also adds CONFIG_SLUB_MEMCG_SYSFS_ON which determines > the boot parameter's default value and defaults to 0. > > ... > > #ifdef CONFIG_MEMCG > - if (is_root_cache(s)) { > + if (is_root_cache(s) && memcg_sysfs_enabled) { This could be turned on and off after bootup but I guess the result could be pretty confusing. However there would be useful use cases? The user would normally have this disabled but if he wants to do a bit of debugging then turn this on, create a memcg, have a poke around then turn the feature off again. > s->memcg_kset = kset_create_and_add("cgroup", NULL, &s->kobj); > if (!s->memcg_kset) { > err = -ENOMEM; > @@ -5673,7 +5695,8 @@ static void sysfs_slab_remove(struct kme > return; > > #ifdef CONFIG_MEMCG > - kset_unregister(s->memcg_kset); > + if (s->memcg_kset) > + kset_unregister(s->memcg_kset); kset_unregister(NULL) is legal --- a/mm/slub.c~slub-make-sysfs-directories-for-memcg-sub-caches-optional-fix +++ a/mm/slub.c @@ -5699,8 +5699,7 @@ static void sysfs_slab_remove(struct kme return; #ifdef CONFIG_MEMCG - if (s->memcg_kset) - kset_unregister(s->memcg_kset); + kset_unregister(s->memcg_kset); #endif kobject_uevent(&s->kobj, KOBJ_REMOVE); kobject_del(&s->kobj); _