From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 24 Jan 2005 12:55:18 -0700 From: Grant Grundler Subject: Re: [PATCH] Avoiding fragmentation through different allocator Message-ID: <20050124195518.GA19747@colo.lackof.org> References: <20050120101300.26FA5E598@skynet.csn.ul.ie> <20050121142854.GH19973@logos.cnet> <20050122215949.GD26391@logos.cnet> <20050124122952.GA5739@logos.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050124122952.GA5739@logos.cnet> Sender: owner-linux-mm@kvack.org Return-Path: To: Marcelo Tosatti Cc: Mel Gorman , William Lee Irwin III , Linux Memory Management List , Linux Kernel Mailing List , grundler@parisc-linux.org, jejb@steeleye.com, awilliam@fc.hp.com List-ID: On Mon, Jan 24, 2005 at 10:29:52AM -0200, Marcelo Tosatti wrote: > Grant Grundler and James Bottomley have been working on this area, > they might want to add some comments to this discussion. > > It seems HP (Grant et all) has pursued using big pages on IA64 (64K) > for this purpose. Marcello, That might have been Alex Williamson...but the reasons for 64K pages is to reduce TLB thrashing, not faster IO. On HP ZX1 boxes, SG performance is slightly better (max +5%) when going through the IOMMU than when bypassing it. The IOMMU can perfectly coalesce DMA pages but has a small CPU and DMA cost to do so as well. Otherwise, I totally agree with James. IO devices do scatter-gather pretty well and IO subsystems are tuned for page-size chunk or smaller anyway. ... > > I could keep digging, but I think the bottom line is that having large > > pages generally available rather than a fixed setting is desirable. > > Definately, yes. Thanks for the pointers. Big pages are good for CPU TLB and that's where most of the research has been done. I think IO devices have learned to cope with the fact the alot less has been (or can be for many workloads) done to coalesce IO pages. grant -- 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: aart@kvack.org