From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753503AbYCLAEX (ORCPT ); Tue, 11 Mar 2008 20:04:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751780AbYCLAEO (ORCPT ); Tue, 11 Mar 2008 20:04:14 -0400 Received: from extu-mxob-2.symantec.com ([216.10.194.135]:36856 "EHLO extu-mxob-2.symantec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751597AbYCLAEN (ORCPT ); Tue, 11 Mar 2008 20:04:13 -0400 Date: Tue, 11 Mar 2008 13:05:44 +0000 (GMT) From: Hugh Dickins X-X-Sender: hugh@blonde.site To: Balbir Singh cc: Pavel Emelyanov , Andrew Morton , Sudhir Kumar , YAMAMOTO Takashi , Paul Menage , lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org, taka@valinux.co.jp, linux-mm@kvack.org, David Rientjes , KAMEZAWA Hiroyuki Subject: Re: [PATCH] Move memory controller allocations to their own slabs (v2) In-Reply-To: <47D66865.1080508@linux.vnet.ibm.com> Message-ID: References: <20080311061836.6664.5072.sendpatchset@localhost.localdomain> <47D63E9D.70500@openvz.org> <47D63FB1.7040502@linux.vnet.ibm.com> <47D6443D.9000904@openvz.org> <47D66865.1080508@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Mar 2008, Balbir Singh wrote: > > On my 64 bit powerpc system (structure size could be different on other systems) > > 1. sizeof page_cgroup is 40 bytes > which means kmalloc will allocate 64 bytes > 2. With 4K pagesize SLAB with HWCACHE_ALIGN, 59 objects are packed per slab > 3. With SLUB the value is 102 per slab I expect you got those numbers with 2.6.25-rc4? Towards the end of -rc5 there's a patch from Nick to make SLUB's treatment of HWCACHE_ALIGN the same as SLAB's, so I expect you'd be back to a similar poor density with SLUB too. (But I'm replying without actually testing it out myself.) I think you'd need a strong reason to choose HWCACHE_ALIGN for these. Consider: the (normal configuration) x86_64 struct page size was 56 bytes for a long time (and still is without MEM_RES_CTLR), but we've never inserted padding to make that a round 64 bytes (and they would benefit additionally from some simpler arithmetic, not the case with page_cgroups). Though it's good to avoid unnecessary sharing and multiple cacheline accesses, it's not so good as to justify almost doubling the size of a very very common structure. I think. Hugh