Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756806AbYCYDaj (ORCPT ); Mon, 24 Mar 2008 23:30:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754775AbYCYDab (ORCPT ); Mon, 24 Mar 2008 23:30:31 -0400 Received: from ozlabs.org ([203.10.76.45]:50364 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754793AbYCYDaa (ORCPT ); Mon, 24 Mar 2008 23:30:30 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18408.29107.709577.374424@cargo.ozlabs.ibm.com> Date: Tue, 25 Mar 2008 14:29:55 +1100 From: Paul Mackerras To: David Miller Cc: clameter@sgi.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: larger default page sizes... In-Reply-To: <20080324.133722.38645342.davem@davemloft.net> References: <20080321.145712.198736315.davem@davemloft.net> <20080324.133722.38645342.davem@davemloft.net> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1765 Lines: 46 David Miller writes: > From: Christoph Lameter > Date: Mon, 24 Mar 2008 11:27:06 -0700 (PDT) > > > The move to 64k page size on IA64 is another way that this issue can > > be addressed though. > > This is such a huge mistake I wish platforms such as powerpc and IA64 > would not make such decisions so lightly. The performance advantage of using hardware 64k pages is pretty compelling, on a wide range of programs, and particularly on HPC apps. > The memory wastage is just rediculious. Depends on the distribution of file sizes you have. > I already see several distributions moving to 64K pages for powerpc, > so I want to nip this in the bud before this monkey-see-monkey-do > thing gets any more out of hand. I just tried a kernel compile on a 4.2GHz POWER6 partition with 4 threads (2 cores) and 2GB of RAM, with two kernels. One was configured with 4kB pages and the other with 64kB kernels but they were otherwise identically configured. Here are the times for the same kernel compile (total time across all threads, for a fairly full-featured config): 4kB pages: 444.051s user + 34.406s system time 64kB pages: 419.963s user + 16.869s system time That's nearly 10% faster with 64kB pages -- on a kernel compile. Yes, the fragmentation in the page cache can be a pain in some circumstances, but on the whole I think the performance advantage is worth that pain, particularly for the sort of applications that people will tend to be running on RHEL on Power boxes. Regards, Paul. -- 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/