From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Enberg Subject: Re: [PATCH 08/40] mm: kmem_cache_objsize Date: Fri, 04 May 2007 21:45:55 +0300 Message-ID: <463B7F63.8070508@cs.helsinki.fi> References: <20070504102651.923946304@chello.nl> <20070504103157.215424767@chello.nl> <1178301545.24217.56.camel@twins> <1178302904.2767.6.camel@lappy> <1178303538.2767.9.camel@lappy> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Lameter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, Trond Myklebust , Thomas Graf , David Miller , James Bottomley , Mike Christie , Andrew Morton , Daniel Phillips To: Peter Zijlstra Return-path: Received: from courier.cs.helsinki.fi ([128.214.9.1]:52839 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161600AbXEDSpm (ORCPT ); Fri, 4 May 2007 14:45:42 -0400 In-Reply-To: <1178303538.2767.9.camel@lappy> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, 2007-05-04 at 11:30 -0700, Christoph Lameter wrote: > > Hmmm... Maybe lets have > > > > unsigned kmem_estimate_pages(struct kmem_cache *slab_cache, int objects) > > > > which would calculate the worst case memory scenario for allocation the > > number of indicated objects? On Fri, 4 May 2007, Peter Zijlstra wrote: > Perfectly fine with me, Pekka, any objections? Again, slab has no way of actually estimating how many pages you need for a given number of objects. So we end up calculating some upper bound which doesn't belong in mm/slab.c. I am perfectly okay with: (1) kmem_nr_bytes_per_object which is what Peter has now or alternatively, (2) kmem_nr_objects_per_page which I think Christoph suggested Both of them, the slab knows the answer, and doesn't need to guess. It's up to the caller to figure out what the acceptable upper bound is. Pekka