From: Pavel Begunkov <asml.silence@gmail.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Mina Almasry" <almasrymina@google.com>,
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Subject: Re: [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers
Date: Wed, 8 May 2024 12:30:07 +0100 [thread overview]
Message-ID: <54830914-1ec9-4312-96ad-423ac0aeb233@gmail.com> (raw)
In-Reply-To: <20240507233247.GK4718@ziepe.ca>
On 5/8/24 00:32, Jason Gunthorpe wrote:
> On Tue, May 07, 2024 at 08:35:37PM +0100, Pavel Begunkov wrote:
>> On 5/7/24 18:56, Jason Gunthorpe wrote:
>>> On Tue, May 07, 2024 at 06:25:52PM +0100, Pavel Begunkov wrote:
>>>> On 5/7/24 17:48, Jason Gunthorpe wrote:
>>>>> On Tue, May 07, 2024 at 09:42:05AM -0700, Mina Almasry wrote:
>>>>>
>>>>>> 1. Align with devmem TCP to use udmabuf for your io_uring memory. I
>>>>>> think in the past you said it's a uapi you don't link but in the face
>>>>>> of this pushback you may want to reconsider.
>>>>>
>>>>> dmabuf does not force a uapi, you can acquire your pages however you
>>>>> want and wrap them up in a dmabuf. No uapi at all.
>>>>>
>>>>> The point is that dmabuf already provides ops that do basically what
>>>>> is needed here. We don't need ops calling ops just because dmabuf's
>>>>> ops are not understsood or not perfect. Fixup dmabuf.
>>>>
>>>> Those ops, for example, are used to efficiently return used buffers
>>>> back to the kernel, which is uapi, I don't see how dmabuf can be
>>>> fixed up to cover it.
>>>
>>> Sure, but that doesn't mean you can't use dma buf for the other parts
>>> of the flow. The per-page lifetime is a different topic than the
>>> refcounting and access of the entire bulk of memory.
>>
>> Ok, so if we're leaving uapi (and ops) and keep per page/sub-buffer as
>> is, the rest is resolving uptr -> pages, and passing it to page pool in
>> a convenient to page pool format (net_iov).
>
> I'm not going to pretend to know about page pool details, but dmabuf
> is the way to get the bulk of pages into a pool within the net stack's
> allocator and keep that bulk properly refcounted while.>
> An object like dmabuf is needed for the general case because there are
> not going to be per-page references or otherwise available.
They are already pinned, memory is owned by the provider, io_uring
in this case, and it should not be freed circumventing io_uring,
and at this stage calling release_pages() is not such a hassle,
especially comparing to introducing an additional object.
My question is how having an intermediary dmabuf benefits the net
stack or io_uring ? For now IMO it doesn't solve anything but adds
extra complexity. Adding dmabuf for the sake of adding dmabuf is
not a great choice.
> What you seem to want is to alter how the actual allocation flow works
> from that bulk of memory and delay the free. It seems like a different
For people who jumped here without looking what this patchset is
about, that's the entire point of the io_uring zero copy approach
as well as this set. Instead of using kernel private pages that you
have no other option but to copy/mmap (and then free), it hands
buffers to the user while using memory accessible/visible in some
way by the user.
That "delay free" is taking a reference while user is reading data
(slightly different for devmem tcp). And note, it's not a page/dmabuf
reference, kernel can forcibly take it back and release pages.
> topic to me, and honestly hacking into the allocator free function
> seems a bit weird..
Do you also think that DMA_BUF_IOCTL_SYNC is a weird hack, because
it "delays free" by pinning the dmabuf object and letting the user
read memory instead of copying it? I can find many examples
--
Pavel Begunkov
next prev parent reply other threads:[~2024-05-08 11:30 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 0:20 [RFC PATCH net-next v8 00/14] Device Memory TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 01/14] queue_api: define queue api Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 02/14] net: page_pool: create hooks for custom page providers Mina Almasry
2024-05-01 7:54 ` Christoph Hellwig
2024-05-03 20:10 ` Mina Almasry
2024-05-06 12:04 ` Christoph Hellwig
2024-05-07 16:05 ` Pavel Begunkov
2024-05-07 16:18 ` Jason Gunthorpe
2024-05-07 16:23 ` Christoph Hellwig
2024-05-07 16:42 ` Mina Almasry
2024-05-07 16:48 ` Jason Gunthorpe
2024-05-07 17:19 ` Daniel Vetter
2024-05-07 17:25 ` Pavel Begunkov
2024-05-07 17:56 ` Jason Gunthorpe
2024-05-07 19:35 ` Pavel Begunkov
2024-05-07 23:32 ` Jason Gunthorpe
2024-05-08 7:16 ` Daniel Vetter
2024-05-08 11:35 ` Pavel Begunkov
2024-05-08 15:34 ` Daniel Vetter
2024-05-08 15:51 ` Christoph Hellwig
2024-05-08 17:02 ` Pavel Begunkov
2024-05-09 4:49 ` Christoph Hellwig
2024-05-08 11:30 ` Pavel Begunkov [this message]
2024-05-08 14:25 ` Jason Gunthorpe
2024-05-08 15:44 ` Pavel Begunkov
2024-05-08 15:58 ` Jason Gunthorpe
2024-05-08 16:13 ` Pavel Begunkov
2024-05-07 17:17 ` Pavel Begunkov
2024-05-07 16:55 ` Pavel Begunkov
2024-05-07 17:15 ` Mina Almasry
2024-05-07 17:34 ` Pavel Begunkov
2024-04-03 0:20 ` [RFC PATCH net-next v8 03/14] net: netdev netlink api to bind dma-buf to a net device Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 04/14] netdev: support binding dma-buf to netdevice Mina Almasry
2024-04-24 17:35 ` David Wei
2024-04-24 22:11 ` Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 05/14] netdev: netdevice devmem allocator Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 06/14] page_pool: convert to use netmem Mina Almasry
2024-04-03 17:27 ` Simon Horman
2024-04-03 0:20 ` [RFC PATCH net-next v8 07/14] page_pool: devmem support Mina Almasry
2024-04-27 0:17 ` David Wei
2024-04-27 2:11 ` Mina Almasry
2024-04-30 13:31 ` Pavel Begunkov
2024-04-30 13:45 ` Jens Axboe
2024-04-30 18:29 ` Mina Almasry
2024-04-30 18:55 ` Jens Axboe
2024-04-30 19:19 ` Mina Almasry
2024-05-01 13:58 ` Jesper Dangaard Brouer
2024-05-01 7:55 ` Christoph Hellwig
2024-05-06 0:29 ` David Wei
2024-04-03 0:20 ` [RFC PATCH net-next v8 08/14] memory-provider: dmabuf devmem memory provider Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 09/14] net: support non paged skb frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 10/14] net: add support for skbs with unreadable frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 11/14] tcp: RX path for devmem TCP Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 12/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags Mina Almasry
2024-04-03 0:20 ` [RFC PATCH net-next v8 13/14] net: add devmem TCP documentation Mina Almasry
2024-05-03 13:14 ` Bagas Sanjaya
2024-04-03 0:20 ` [RFC PATCH net-next v8 14/14] selftests: add ncdevmem, netcat for devmem TCP Mina Almasry
2024-04-08 15:57 ` Cong Wang
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