From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 1 Mar 2007 21:53:42 -0800 (PST) From: Christoph Lameter Subject: Re: The performance and behaviour of the anti-fragmentation related patches In-Reply-To: <20070302054944.GE15867@wotan.suse.de> Message-ID: References: <20070301101249.GA29351@skynet.ie> <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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: 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 List-ID: On Fri, 2 Mar 2007, Nick Piggin wrote: > > You do not have to deal with TLB entries if you do buffered I/O. > > Where does the data come from? >>From the I/O controller and from the application. > > We currently have problems with the kernel limits of 128 SG > > entries but the fundamental issue is that we can only do 2 Meg of I/O in > > one go given the default limits of the block layer. Typically the number > > of hardware SG entrie is also limited. We never will be able to put a > > Seems like changing the default limits would be the easiest way to > fix it then? This would only be a temporary fix pushing the limits to the double or so? > As far as hardware limits go, I don't think you need to scale that > number linearly with the amount of memory you have, or even with the > IO throughput. You should reach a point where your command overhead > is amortised sufficiently, and the controller will be pipelining the > commands. 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org