From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Date: Tue, 12 Sep 2006 06:40:22 +0000 Subject: Re: [PATCH 5/6] Optional ZONE_DMA for x86_64 Message-Id: <200609120840.22808.ak@suse.de> List-Id: References: <20060911222755.4849.17749.sendpatchset@schroedinger.engr.sgi.com> In-Reply-To: <20060911222755.4849.17749.sendpatchset@schroedinger.engr.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Tuesday 12 September 2006 00:27, Christoph Lameter wrote: > x86_64: optional ZONE_DMA/ZONE_DMA32 > > Allow the use to specify CONFIG_ZONE_DMA32 and CONFIG_ZONE_DMA (via > CONFIG_GENERIC_ISA_DMA). > > If CONFIG_ZONE_DMA is off then devices requiring ISA DMA can no > longer be selected. > > There are no drivers depending on CONFIG_ZONE_DMA32. If CONFIG_ZONE_DMA32 > is not set then the system assumes that DMA devices are capable of > doing DMA to all of memory (which is mostly the case since most > x86_64 motherboards only allow a max of 4GB of memory and advanced > systems have DMA subsystems that handle I/O properly). Pretty much all have this problem (or do you know of a system with no USB controller?) I think I would prefer to not make GFP_DMA32 optional. Adding a 4GB limit CONFIG to a 64bit kernel just seems somewhat dumb. Also what happens when someone still sets GFP_DMA? iirc the SCSI stack tended to do that for some structures. Will it fail? Making GFP_DMA optional would be an interesting experiment (I think it will break the floppies but other than that a modern system might be fine). But it would be better to warn the user stronger against it (most likely it will still break a lot of older addin cards) and tell them about the floppy. BTW we still call it x86-64, not x64. -Andi