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b=r8FDZ/eqWYdwVV33jxNOmMZ+Q0AP3rwSmcV0uxmnDzV9AH8VKsm2AhWHfGWT889lo PW2S6gzgMKo/i1iegkaYaSZLbOP2NGoCHvp3W7C1SEA2tSAaX2lt7VyWeuc+yOj4mQ 67y7RizelJUGDFaDnVc8Ca5FC/Md3RUStChth9FSRxA9a6gJGOg/Stl6BWAUBQzxag Twhnp6n0rEZppEbaPBRq1/2VoVWeiqojRDHjfmv0v6MA4DTJRvSa7ZT+Swdukz92mb x0y8++/TZxgW1mputNaBFh0nXeVl32Wp9zMYS8ldM65ag6zt7ha5AlkXuQ0NINARHO ZxDtxobQwvtIQ== Date: Sun, 2 Feb 2025 10:22:23 +0200 From: Leon Romanovsky To: Jason Gunthorpe Cc: Alistair Popple , linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org, david@redhat.com, willy@infradead.org, ziy@nvidia.com, jhubbard@nvidia.com, balbirs@nvidia.com Subject: Re: [LSF/MM/BPF TOPIC] The future of ZONE_DEVICE pages Message-ID: <20250202082223.GA3359673@unreal> References: <20250131145237.GQ5556@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <20250131145237.GQ5556@nvidia.com> X-Rspamd-Queue-Id: 9189B1C0003 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: qiz1sbybesnhzfynsfbw8mm4crw63xsk X-HE-Tag: 1738484549-626241 X-HE-Meta: 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 mDloM3Oh 60mBrnyHETiRqn+amgMN9jk3WycfB9pv+iVfM2Kr3Y62JoG48TlghCVhZoZrQWhZQC2uuWU3Ppm+Gc9TI5/7K7k4PzosSb79yk8nTiyOWfyWb88PEfWPiBmhJQ23PqOvLCOYS0genC/1BWIxvOkUjkgJjel/bPORvt7ZwamOaACXtCGi5kpX2SxhSgt3cqSpLeAJWkyvm+taw/hc+5hS5vl9g0i60Wwk22WKkj3GToYF1qtJvhHIoP0IZBdOKtzKq8qOgo9UDKubD1D5PIhtpjy/lAm2M5Yy9lFZK0dqQBwDWGnfeXfNdLdZwVCcrNZUN62aR0to7YdSUgYkWUiDxWHj6lA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 31, 2025 at 10:52:37AM -0400, Jason Gunthorpe wrote: > On Fri, Jan 31, 2025 at 01:59:09PM +1100, Alistair Popple wrote: > > Combining P2PDMA and DEVICE_PRIVATE pages > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > >=20 > > Currently device memory that cannot be directly accessed via the CPU ca= n be > > represented by DEVICE_PRIVATE pages allowing it to be mapped and treate= d like > > a normal virtual page by userpsace. Many devices also support accessing= device > > memory directly from the CPU via a PCIe BAR. > >=20 > > This access requires a P2PDMA page, meaning there are potentially two p= ages > > tracking the same piece of physical memory. This not only seems wastefu= l but > > fraught - for example device drivers need to keep page lifetimes in syn= c. I > > would like to discuss ways of solving this. >=20 > My general plan for this has been to teach the DMA API how to do P2P > without struct page. Leon's topic is the frist step on this journey. > https://lore.kernel.org/linux-mm/97f385db-42c9-4c04-8fba-9b1ba8ffc525@n= vidia.com/ The latest proposal for LSF/MM 2025 is here: [LSF/MM/BPF TOPIC] DMA mapping API in complex scenarios https://lore.kernel.org/linux-rdma/20250122071600.GC10702@unreal/T/#u Thanks