Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753771AbaFKVYz (ORCPT ); Wed, 11 Jun 2014 17:24:55 -0400 Received: from mx2.parallels.com ([199.115.105.18]:41183 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752501AbaFKVYy (ORCPT ); Wed, 11 Jun 2014 17:24:54 -0400 Date: Thu, 12 Jun 2014 01:24:34 +0400 From: Vladimir Davydov To: Christoph Lameter CC: Joonsoo Kim , , , , , , , Subject: Re: [PATCH -mm v2 8/8] slab: make dead memcg caches discard free slabs immediately Message-ID: <20140611212431.GA16589@esperanza> References: <27a202c6084d6bb19cc3e417793f05104b908ded.1402060096.git.vdavydov@parallels.com> <20140610074317.GE19036@js1304-P5Q-DELUXE> <20140610100313.GA6293@esperanza> <20140610151830.GA8692@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20140610151830.GA8692@esperanza> X-Originating-IP: [81.5.110.170] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 10, 2014 at 07:18:34PM +0400, Vladimir Davydov wrote: > On Tue, Jun 10, 2014 at 09:26:19AM -0500, Christoph Lameter wrote: > > On Tue, 10 Jun 2014, Vladimir Davydov wrote: > > > > > Frankly, I incline to shrinking dead SLAB caches periodically from > > > cache_reap too, because it looks neater and less intrusive to me. Also > > > it has zero performance impact, which is nice. > > > > > > However, Christoph proposed to disable per cpu arrays for dead caches, > > > similarly to SLUB, and I decided to give it a try, just to see the end > > > code we'd have with it. > > > > > > I'm still not quite sure which way we should choose though... > > > > Which one is cleaner? > > To shrink dead caches aggressively, we only need to modify cache_reap > (see https://lkml.org/lkml/2014/5/30/271). Hmm, reap_alien, which is called from cache_reap to shrink per node alien object arrays, only processes one node at a time. That means with the patch I gave a link to above it will take up to (REAPTIMEOUT_AC*nr_online_nodes) seconds to destroy a virtually empty dead cache, which may be quite long on large machines. Of course, we can make reap_alien walk over all alien caches of the current node, but that will probably hurt performance... > > To zap object arrays for dead caches (this is what this patch does), we > have to: > - set array_cache->limit to 0 for each per cpu, shared, and alien array > caches on kmem_cache_shrink; > - make cpu/node hotplug paths init new array cache sizes to 0; > - make free paths (__cache_free, cache_free_alien) handle zero array > cache size properly, because currently they doesn't. > > So IMO the first one (reaping dead caches periodically) requires less > modifications and therefore is cleaner. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/