Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753820AbZCIJOQ (ORCPT ); Mon, 9 Mar 2009 05:14:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752927AbZCIJNZ (ORCPT ); Mon, 9 Mar 2009 05:13:25 -0400 Received: from smtp-out.google.com ([216.239.33.17]:33806 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753365AbZCIJNV (ORCPT ); Mon, 9 Mar 2009 05:13:21 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id: references:user-agent:mime-version:content-type:x-system-of-record; b=bAVh127a46WoSfUcHe51DGK4jQg0M/QJbuhrlCf+DollKJd4N77ohbkNQxCbcbk08 wdTFx49hDGCheDiYHeTlw== Date: Mon, 9 Mar 2009 02:12:21 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: KOSAKI Motohiro cc: Andrew Morton , Christoph Lameter , Pekka Enberg , Matt Mackall , Paul Menage , Randy Dunlap , linux-kernel@vger.kernel.org Subject: Re: [patch -mm] cpusets: add memory_slab_hardwall flag In-Reply-To: <20090309123011.A228.A69D9226@jp.fujitsu.com> Message-ID: References: <20090309123011.A228.A69D9226@jp.fujitsu.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1352 Lines: 30 On Mon, 9 Mar 2009, KOSAKI Motohiro wrote: > Hmmm, > this description only explay how to implement this. > but no explain why this patch is useful. > > Could you please who and why need it? > The change to Documentation/cgroups/cpusets.txt should have explained it. This is for two cases: true memory isolation (now including slab allocations at the object level) and NUMA optimizations. Prior to this change, it was possible for slabs to be allocated in a cpuset while its objects were largely consumed by disjoint cpusets. We can fix that by only allocating objects from slabs that are found on current->mems_allowed. While this incurs a performance penalty, some users may find that true isolation outweighs the cache optimizations. It is also helpful for long-lived objects that require NUMA affinity to a certain cpu or group of cpus. That is, after all, the reasoning behind cpusets in the first place. If slab objects were all allocated from a node with remote affinity to the cpus that will be addressing it, it negates a significant advantage that cpusets provides to the user. -- 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/