From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 26 Jan 2007 11:46:15 -0800 From: Andrew Morton Subject: Re: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages Message-Id: <20070126114615.5aa9e213.akpm@osdl.org> In-Reply-To: References: <20070125234458.28809.5412.sendpatchset@skynet.skynet.ie> <20070126030753.03529e7a.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter List-ID: On Fri, 26 Jan 2007 07:56:09 -0800 (PST) Christoph Lameter wrote: > On Fri, 26 Jan 2007, Andrew Morton wrote: > > > - They add zillions of ifdefs > > They just add a few for ZONE_DMA where we alreaday have similar ifdefs for > ZONE_DMA32 and ZONE_HIGHMEM. I refreshed my memory. It remains awful. > > - They make the VM's behaviour diverge between different platforms and > > between differen configs on the same platforms, and hence degrade > > maintainability and increase complexity. > > They avoid unecessary complexity on platforms. They could be made to work > on more platforms with measures to deal with what ZONE_DMA > provides in different ways. There are 6 or so platforms that do not need > ZONE_DMA at all. As Mel points out, distros will ship with CONFIG_ZONE_DMA=y, so the number of machines which will actually benefit from this change is really small. And the benefit to those few machines will also, I suspect, be small. > > - We kicked around some quite different ways of implementing the same > > things, but nothing came of it. iirc, one was to remove the hard-coded > > zones altogether and rework all the MM to operate in terms of > > > > for (idx = 0; idx < NUMBER_OF_ZONES; idx++) > > ... > > Hmmm.. How would that be simpler? Replace a sprinkle of open-coded ifdefs with a regular code sequence which everyone uses. Pretty obvious, I'd thought. Plus it becoems straightforward to extend this from the present four zones to a complete 12 zones, which gives use the full set of ZONE_DMA20,ZONE_DMA21,...,ZONE_DMA32 for those funny devices. > > - I haven't seen any hard numbers to justify the change. > > I have send you numbers showing significant reductions in code size. If it isn't in the changelog it doesn't exist. I guess I didn't copy it into the changelog. If the only demonstrable benefit is a saving of a few k of text on a small number of machines then things are looking very grim, IMO. -- 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