From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 09CCF6B0069 for ; Thu, 20 Oct 2016 23:44:39 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id u84so42308004pfj.6 for ; Thu, 20 Oct 2016 20:44:39 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id x67si651385pfb.20.2016.10.20.20.44.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Oct 2016 20:44:38 -0700 (PDT) Date: Thu, 20 Oct 2016 20:44:35 -0700 From: Andrew Morton Subject: Re: [PATCH 1/2] mm: memcontrol: use special workqueue for creating per-memcg caches Message-Id: <20161020204435.5e0ffca43c7b6ab5f69d692a@linux-foundation.org> In-Reply-To: <20161004131417.GC1862@esperanza> References: <20161003120641.GC26768@dhcp22.suse.cz> <20161003123505.GA1862@esperanza> <20161003131930.GE26768@dhcp22.suse.cz> <20161004131417.GC1862@esperanza> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, 4 Oct 2016 16:14:17 +0300 Vladimir Davydov wrote: > Creating a lot of cgroups at the same time might stall all worker > threads with kmem cache creation works, because kmem cache creation is > done with the slab_mutex held. The problem was amplified by commits > 801faf0db894 ("mm/slab: lockless decision to grow cache") in case of > SLAB and 81ae6d03952c ("mm/slub.c: replace kick_all_cpus_sync() with > synchronize_sched() in kmem_cache_shrink()") in case of SLUB, which > increased the maximal time the slab_mutex can be held. > > To prevent that from happening, let's use a special ordered single > threaded workqueue for kmem cache creation. This shouldn't introduce any > functional changes regarding how kmem caches are created, as the work > function holds the global slab_mutex during its whole runtime anyway, > making it impossible to run more than one work at a time. By using a > single threaded workqueue, we just avoid creating a thread per each > work. Ordering is required to avoid a situation when a cgroup's work is > put off indefinitely because there are other cgroups to serve, in other > words to guarantee fairness. I'm having trouble working out the urgency of this patch? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org