From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f72.google.com (mail-lf0-f72.google.com [209.85.215.72]) by kanga.kvack.org (Postfix) with ESMTP id 54DAA6B0038 for ; Fri, 27 Jan 2017 13:03:13 -0500 (EST) Received: by mail-lf0-f72.google.com with SMTP id x1so110367335lff.6 for ; Fri, 27 Jan 2017 10:03:13 -0800 (PST) Received: from smtp54.i.mail.ru (smtp54.i.mail.ru. [217.69.128.34]) by mx.google.com with ESMTPS id g38si3306583lfi.85.2017.01.27.10.03.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Jan 2017 10:03:11 -0800 (PST) Date: Fri, 27 Jan 2017 21:03:05 +0300 From: Vladimir Davydov Subject: Re: [PATCH 03/10] slab: remove synchronous rcu_barrier() call in memcg cache release path Message-ID: <20170127180305.GB4332@esperanza> References: <20170117235411.9408-1-tj@kernel.org> <20170117235411.9408-4-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170117235411.9408-4-tj@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, jsvana@fb.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@fb.com On Tue, Jan 17, 2017 at 03:54:04PM -0800, Tejun Heo wrote: > With kmem cgroup support enabled, kmem_caches can be created and > destroyed frequently and a great number of near empty kmem_caches can > accumulate if there are a lot of transient cgroups and the system is > not under memory pressure. When memory reclaim starts under such > conditions, it can lead to consecutive deactivation and destruction of > many kmem_caches, easily hundreds of thousands on moderately large > systems, exposing scalability issues in the current slab management > code. This is one of the patches to address the issue. > > SLAB_DESTORY_BY_RCU caches need to flush all RCU operations before > destruction because slab pages are freed through RCU and they need to > be able to dereference the associated kmem_cache. Currently, it's > done synchronously with rcu_barrier(). As rcu_barrier() is expensive > time-wise, slab implements a batching mechanism so that rcu_barrier() > can be done for multiple caches at the same time. > > Unfortunately, the rcu_barrier() is in synchronous path which is > called while holding cgroup_mutex and the batching is too limited to > be actually helpful. > > This patch updates the cache release path so that the batching is > asynchronous and global. All SLAB_DESTORY_BY_RCU caches are queued > globally and a work item consumes the list. The work item calls > rcu_barrier() only once for all caches that are currently queued. > > * release_caches() is removed and shutdown_cache() now either directly > release the cache or schedules a RCU callback to do that. This > makes the cache inaccessible once shutdown_cache() is called and > makes it impossible for shutdown_memcg_caches() to do memcg-specific > cleanups afterwards. Move memcg-specific part into a helper, > unlink_memcg_cache(), and make shutdown_cache() call it directly. > > Signed-off-by: Tejun Heo > Reported-by: Jay Vana > Cc: Vladimir Davydov > Cc: Christoph Lameter > Cc: Pekka Enberg > Cc: David Rientjes > Cc: Joonsoo Kim > Cc: Andrew Morton Acked-by: Vladimir Davydov -- 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