From: Jason Gunthorpe <jgg@ziepe.ca>
To: Alistair Popple <apopple@nvidia.com>
Cc: "Matthew Wilcox" <willy@infradead.org>,
"Yonatan Maman" <ymaman@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Leon Romanovsky" <leon@kernel.org>,
"Lyude Paul" <lyude@redhat.com>,
"Danilo Krummrich" <dakr@kernel.org>,
"David Airlie" <airlied@gmail.com>,
"Simona Vetter" <simona@ffwll.ch>,
"Ben Skeggs" <bskeggs@nvidia.com>,
"Michael Guralnik" <michaelgur@nvidia.com>,
"Or Har-Toov" <ohartoov@nvidia.com>,
"Daisuke Matsuda" <dskmtsd@gmail.com>,
"Shay Drory" <shayd@nvidia.com>,
linux-mm@kvack.org, linux-rdma@vger.kernel.org,
dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
linux-kernel@vger.kernel.org, "Gal Shalom" <GalShalom@nvidia.com>
Subject: Re: [PATCH v2 1/5] mm/hmm: HMM API to enable P2P DMA for device private pages
Date: Wed, 23 Jul 2025 00:51:42 -0300 [thread overview]
Message-ID: <aIBcTpC9Te7YIe4J@ziepe.ca> (raw)
In-Reply-To: <7lvduvov3rvfsgixbkyyinnzz3plpp3szxam46ccgjmh6v5d7q@zoz4k723vs3d>
On Tue, Jul 22, 2025 at 10:49:10AM +1000, Alistair Popple wrote:
> > So what is it?
>
> IMHO a hack, because obviously we shouldn't require real physical addresses for
> something the CPU can't actually address anyway and this causes real
> problems
IMHO what DEVICE PRIVATE really boils down to is a way to have swap
entries that point to some kind of opaque driver managed memory.
We have alot of assumptions all over about pfn/phys to page
relationships so anything that has a struct page also has to come with
a fake PFN today..
> (eg. it doesn't actually work on anything other than x86_64). There's no reason
> the "PFN" we store in device-private entries couldn't instead just be an index
> into some data structure holding pointers to the struct pages. So instead of
> using pfn_to_page()/page_to_pfn() we would use device_private_index_to_page()
> and page_to_device_private_index().
It could work, but any of the pfn conversions would have to be tracked
down.. Could be troublesome.
Jason
next prev parent reply other threads:[~2025-07-23 3:51 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-18 11:51 [PATCH v2 0/5] *** GPU Direct RDMA (P2P DMA) for Device Private Pages *** Yonatan Maman
2025-07-18 11:51 ` [PATCH v2 1/5] mm/hmm: HMM API to enable P2P DMA for device private pages Yonatan Maman
2025-07-18 14:17 ` Matthew Wilcox
2025-07-18 14:44 ` Jason Gunthorpe
2025-07-21 0:11 ` Alistair Popple
2025-07-21 13:23 ` Matthew Wilcox
2025-07-22 0:49 ` Alistair Popple
2025-07-23 3:51 ` Jason Gunthorpe [this message]
2025-07-23 4:10 ` Alistair Popple
2025-07-24 8:52 ` David Hildenbrand
2025-07-25 0:31 ` Alistair Popple
2025-07-25 9:51 ` David Hildenbrand
2025-08-01 16:40 ` Jason Gunthorpe
2025-08-01 16:50 ` David Hildenbrand
2025-08-01 16:57 ` Jason Gunthorpe
2025-08-04 1:51 ` Alistair Popple
2025-08-05 14:09 ` Jason Gunthorpe
2025-08-04 7:48 ` David Hildenbrand
2025-07-21 6:59 ` Christoph Hellwig
2025-07-22 5:42 ` Yonatan Maman
2025-08-01 16:52 ` Jason Gunthorpe
2025-07-18 11:51 ` [PATCH v2 2/5] nouveau/dmem: HMM P2P DMA for private dev pages Yonatan Maman
2025-07-21 7:00 ` Christoph Hellwig
2025-07-22 5:23 ` Yonatan Maman
2025-07-18 11:51 ` [PATCH v2 3/5] IB/core: P2P DMA for device private pages Yonatan Maman
2025-07-18 11:51 ` [PATCH v2 4/5] RDMA/mlx5: Enable P2P DMA with fallback mechanism Yonatan Maman
2025-07-21 7:03 ` Christoph Hellwig
2025-07-23 3:55 ` Jason Gunthorpe
2025-07-24 7:30 ` Christoph Hellwig
2025-08-01 16:46 ` Jason Gunthorpe
2025-07-18 11:51 ` [PATCH v2 5/5] RDMA/mlx5: Enabling ATS for ODP memory Yonatan Maman
2025-07-20 10:30 ` [PATCH v2 0/5] *** GPU Direct RDMA (P2P DMA) for Device Private Pages *** Leon Romanovsky
2025-07-20 21:03 ` Yonatan Maman
2025-07-21 6:49 ` Leon Romanovsky
2025-07-23 4:03 ` Jason Gunthorpe
2025-07-23 8:44 ` Leon Romanovsky
2025-07-21 6:54 ` Christoph Hellwig
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