Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932334AbWAWUYH (ORCPT ); Mon, 23 Jan 2006 15:24:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932466AbWAWUYH (ORCPT ); Mon, 23 Jan 2006 15:24:07 -0500 Received: from kanga.kvack.org ([66.96.29.28]:3980 "EHLO kanga.kvack.org") by vger.kernel.org with ESMTP id S932334AbWAWUYF (ORCPT ); Mon, 23 Jan 2006 15:24:05 -0500 Date: Mon, 23 Jan 2006 15:19:50 -0500 From: Benjamin LaHaise To: Dave McCracken Cc: Hugh Dickins , Andrew Morton , Linux Kernel , Linux Memory Management Subject: Re: [PATCH/RFC] Shared page tables Message-ID: <20060123201950.GI1008@kvack.org> References: <6F40FCDC9FFDE7B6ACD294F5@[10.1.1.4]> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6F40FCDC9FFDE7B6ACD294F5@[10.1.1.4]> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1479 Lines: 28 On Mon, Jan 23, 2006 at 11:39:07AM -0600, Dave McCracken wrote: > The pmd level is important for ppc because it works in segments, which are > 256M in size and consist of a full pmd page. The current implementation of > the way ppc loads its tlb doesn't allow sharing at smaller than segment > size. I currently also enable pmd sharing for x86_64, but I'm not sure how > much of a win it is. I use it to share pmd pages for hugetlb, as well. For EM64T at least, pmd sharing is definately worthwhile. pud sharing is a bit more out there, but would still help database workloads. In the case of a thousand connections (which is not unreasonable for some users) you save 4MB of memory and reduce the cache footprint of those saved 4MB of pages to 4KB. Ideally the code can be structured to compile out to nothing if not needed. Of course, once we have shared page tables it makes great sense to try to get userland to align code segments and data segments to seperate puds so that we could share all the page tables for common system libraries amongst processes... -ben -- "Ladies and gentlemen, I'm sorry to interrupt, but the police are here and they've asked us to stop the party." Don't Email: . - 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/