From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422948AbXCBGTu (ORCPT ); Fri, 2 Mar 2007 01:19:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422957AbXCBGTu (ORCPT ); Fri, 2 Mar 2007 01:19:50 -0500 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:59510 "EHLO netops-testserver-3.corp.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1422952AbXCBGTt (ORCPT ); Fri, 2 Mar 2007 01:19:49 -0500 Date: Thu, 1 Mar 2007 22:19:48 -0800 (PST) From: Christoph Lameter To: Nick Piggin cc: Andrew Morton , Mel Gorman , mingo@elte.hu, jschopp@austin.ibm.com, arjan@infradead.org, torvalds@linux-foundation.org, mbligh@mbligh.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: The performance and behaviour of the anti-fragmentation related patches In-Reply-To: <20070302060831.GF15867@wotan.suse.de> Message-ID: References: <20070301160915.6da876c5.akpm@linux-foundation.org> <20070302035751.GA15867@wotan.suse.de> <20070302042149.GB15867@wotan.suse.de> <20070302050625.GD15867@wotan.suse.de> <20070302054944.GE15867@wotan.suse.de> <20070302060831.GF15867@wotan.suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2 Mar 2007, Nick Piggin wrote: > > >From the I/O controller and from the application. > > Why doesn't the application need to deal with TLB entries? Because it may only operate on a small section of the file and hopefully splice the rest through? But yes support for mmapped I/O would be necessary. > > This would only be a temporary fix pushing the limits to the double or so? > > And using slightly larger page sizes isn't? There was no talk about slightly. 1G page size would actually be quite convenient for some applications. > > Amortized? The controller still would have to hunt down the 4kb page > > pieces that we have to feed him right now. Result: Huge scatter gather > > lists that may themselves create issues with higher page order. > > What sort of numbers do you have for these controllers that aren't > very good at doing sg? Writing a terabyte of memory to disk with handling 256 billion page structs? In case of a system with 1 petabyte of memory this may be rather typical and necessary for the application to be able to save its state on disk. > Isn't the issue was something like your IO controllers have only a > limited number of sg entries, which is fine with 16K pages, but with > 4K pages that doesn't give enough data to cover your RAID stripe? > > We're never going to do a variable sized pagecache just because of that. No, we need support for larger page sizes than 16k. 16k has not been fine for a couple of years. We only agreed to 16k because that was the common consensus. Best performance was always at 64k 4 years ago (but then we have no numbers for higher page sizes yet). Now we would prefer much larger sizes.