Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755027AbcDAPsL (ORCPT ); Fri, 1 Apr 2016 11:48:11 -0400 Received: from casper.infradead.org ([85.118.1.10]:51022 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752283AbcDAPsK (ORCPT ); Fri, 1 Apr 2016 11:48:10 -0400 Date: Fri, 1 Apr 2016 17:48:03 +0200 From: Peter Zijlstra To: Vladimir Davydov Cc: Andrew Morton , Christoph Lameter , Joonsoo Kim , Pekka Enberg , David Rientjes , Johannes Weiner , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: slub: replace kick_all_cpus_sync with synchronize_sched in kmem_cache_shrink Message-ID: <20160401154803.GL3448@twins.programming.kicks-ass.net> References: <1459513817-11853-1-git-send-email-vdavydov@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459513817-11853-1-git-send-email-vdavydov@virtuozzo.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1325 Lines: 26 On Fri, Apr 01, 2016 at 03:30:17PM +0300, Vladimir Davydov wrote: > When we call __kmem_cache_shrink on memory cgroup removal, we need to > synchronize kmem_cache->cpu_partial update with put_cpu_partial that > might be running on other cpus. Currently, we achieve that by using > kick_all_cpus_sync, which works as a system wide memory barrier. Though > fast it is, this method has a flow - it issues a lot of IPIs, which > might hurt high performance or real-time workloads. > > To fix this, let's replace kick_all_cpus_sync with synchronize_sched. > Although the latter one may take much longer to finish, it shouldn't be > a problem in this particular case, because memory cgroups are destroyed > asynchronously from a workqueue so that no user visible effects should > be introduced. OTOH, it will save us from excessive IPIs when someone > removes a cgroup. > > Anyway, even if using synchronize_sched turns out to take too long, we > can always introduce a kind of __kmem_cache_shrink batching so that this > method would only be called once per one cgroup destruction (not per > each per memcg kmem cache as it is now). > > Reported-and-suggested-by: Peter Zijlstra > Signed-off-by: Vladimir Davydov Thanks! Acked-by: Peter Zijlstra (Intel)