From: David Hildenbrand <david@redhat.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Alistair Popple" <apopple@nvidia.com>,
"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: Mon, 4 Aug 2025 09:48:15 +0200 [thread overview]
Message-ID: <16c98fa8-e85c-4aa2-bf53-ba070833661c@redhat.com> (raw)
In-Reply-To: <20250801165749.GF26511@ziepe.ca>
On 01.08.25 18:57, Jason Gunthorpe wrote:
> On Fri, Aug 01, 2025 at 06:50:18PM +0200, David Hildenbrand wrote:
>> On 01.08.25 18:40, Jason Gunthorpe wrote:
>>> On Fri, Jul 25, 2025 at 10:31:25AM +1000, Alistair Popple wrote:
>>>
>>>> The only issue would be if there were generic code paths that somehow have a
>>>> raw pfn obtained from neither a page-table walk or struct page. My assumption
>>>> (yet to be proven/tested) is that these paths don't exist.
>>>
>>> hmm does it, it encodes the device private into a pfn and expects the
>>> caller to do pfn to page.
>>>
>>> This isn't set in stone and could be changed..
>>>
>>> But broadly, you'd want to entirely eliminate the ability to go from
>>> pfn to device private or from device private to pfn.
>>>
>>> Instead you'd want to work on some (space #, space index) tuple, maybe
>>> encoded in a pfn_t, but absolutely and typesafely distinct. Each
>>> driver gets its own 0 based space for device private information, the
>>> space is effectively the pgmap.
>>>
>>> And if you do this, maybe we don't need struct page (I mean the type!)
>>> backing device memory at all.... Which would be a very worthwhile
>>> project.
>>>
>>> Do we ever even use anything in the device private struct page? Do we
>>> refcount it?
>>
>> ref-counted and map-counted ...
>
> Hm, so it would turn into another struct page split up where we get
> ourselves a struct device_private and change all the places touching
> its refcount and mapcount to use the new type.
We're already working with folios in all cases where we modify either
refcount or mapcount IIUC.
The rmap handling (try to migrate, soon folio splitting) currently
depends on the mapcount.
Not sure how that will all look like without a ... struct folio / struct
page.
--
Cheers,
David / dhildenb
next prev parent reply other threads:[~2025-08-04 7:48 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
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 [this message]
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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