From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: GFP_DMA use in SCSI midlayer Date: Mon, 2 Oct 2006 21:18:46 +0200 Message-ID: <200610022118.46830.ak@suse.de> References: <200610012213.24123.ak@suse.de> <200610012255.49802.ak@suse.de> <1159800770.3460.11.camel@mulgrave.il.steeleye.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Return-path: Received: from mx2.suse.de ([195.135.220.15]:58798 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S965355AbWJBTSv (ORCPT ); Mon, 2 Oct 2006 15:18:51 -0400 In-Reply-To: <1159800770.3460.11.camel@mulgrave.il.steeleye.com> Content-Disposition: inline Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: linux-scsi@vger.kernel.org, Christoph Lameter On Monday 02 October 2006 16:52, James Bottomley wrote: > On Sun, 2006-10-01 at 22:55 +0200, Andi Kleen wrote: > > This means the majority of drivers will never use it? I don't > > claim to be a SCSI expert, but a lot of uses looked unchecked > > to me from a quick look. That is very worrying because it's > > only 16MB on x86 and 16MB run out quickly. > > Yes, some cases it's used because the code can't be bothered to check to > see if it's required ... these cases can be audited and cleaned up. That would be useful. > > If it's never used I don't care that much, but it certainly > > doesn't look like that. > > > > Or do you only need it because pci_map_single() on i386 doesn't > > do bouncing? If yes we can probably fix that. > > Heh, that would be the worst place to fix it. We usually have use > context for the allocation, so can sleep in the worst case. We don't > have such context where we do pci_map_single(). Ok then you'll likely want a new function that does this. Do you always have a device or is a mask enough? > > > However, what is wanted in every case is > > > ordinary memory, not coherent memory. They can't simply be replaced > > > with dma_alloc_coherent because > > > > > > a) it will waste memory for platforms that only do it in page size > > > multiples > > > b) It will fail on platforms that can't do it at all. > > > > GFP_DMA will also fail on a lot of platforms, so it's the same. > > No, at the moment it succeeds on all of them (although at odd locations, > like on parisc GFP_DMA goes up to 4GB). Not after Christoph's patchkit went in. -Andi