From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love Date: Sat, 28 Apr 2018 01:33:47 -0700 Message-ID: <20180428083347.GC31684@infradead.org> References: <20180426215406.GB27853@wotan.suse.de> <20180427053556.GB11339@infradead.org> <20180427071843.GB17484@dhcp22.suse.cz> <20180427161813.GD8161@bombadil.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Matthew Wilcox , Michal Hocko , Christoph Hellwig , "Luis R. Rodriguez" , linux-mm@kvack.org, Jan Kara , matthew@wil.cx, x86@kernel.org, luto@amacapital.net, martin.petersen@oracle.com, jthumshirn@suse.de, broonie@kernel.org, linux-spi@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, "lsf-pc@lists.linux-foundation.org" To: Christopher Lameter Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org On Fri, Apr 27, 2018 at 11:36:23AM -0500, Christopher Lameter wrote: > On Fri, 27 Apr 2018, Matthew Wilcox wrote: > > > Some devices have incredibly bogus hardware like 28 bit addressing > > or 39 bit addressing. We don't have a good way to allocate memory by > > physical address other than than saying "GFP_DMA for anything less than > > 32, GFP_DMA32 (or GFP_KERNEL on 32-bit) for anything less than 64 bit". > > > > Even CMA doesn't have a "cma_alloc_phys()". Maybe that's the right place > > to put such an allocation API. > > The other way out of this would be to require a IOMMU? Which on many systems doesn't exist. And even if it exists might not be usable.