From: Pavel Begunkov <asml.silence@gmail.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Mina Almasry" <almasrymina@google.com>,
"Christoph Hellwig" <hch@infradead.org>,
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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 16:44:32 +0100 [thread overview]
Message-ID: <6f69694b-4281-45a6-92aa-d9d72b918df2@gmail.com> (raw)
In-Reply-To: <20240508142530.GR4718@ziepe.ca>
On 5/8/24 15:25, Jason Gunthorpe wrote:
> On Wed, May 08, 2024 at 12:30:07PM +0100, Pavel Begunkov wrote:
>
>>> 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.
>
> Something needs to co-ordinate when the net stack's allocator is done
> with the bulk of pages and when io_uring and do the final
> put_user_page() to free it. DMABUF is not an unreasonable choice for
> this.
When a page pool dies notifies io_uring via the ->destroy callback.
Vise versa, when io_uring wants to terminate zerocopy, it releases
the interface queue, which kills the page pool, ending in
->destroy again.
>>> 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
>
> It seems to me the flow you want is for the driver to allocate a page,
> put it on a rx ring, process it through the netstack, and deliver it
> to io_uring. io_uring would then sit on the allocation until userspace
> it done and return it back to the netstack allocator.
That's right, with a note that "driver allocating a page" is
not a alloc_page() but grabbing a user page/frag the user
registered beforehand.
> Hooking the free of the netstack allocator and then defering it seems
FWIW, it's not about page pool's ->release_page, it's a slow
path and in an ideal world wouldn't be called outside of tear
down.
> like a weird and indirect way to get there. Why can't io_uring just be
> the entity that does the final free and not mess with the logic
> allocator?
Then the user has to do a syscall (e.g. via io_uring) to return pages,
and there we'd need to care how to put the pages efficiently, i.e.
hitting the page pool's fast path, e.g. by hoping napi is scheduled and
scheduled for the CPU we're running on, or maybe transferring the pages
to the right CPU first.
Compare it with userspace putting pages into a ring, and the allocator
taking from there when needed without any extra synchronisation and
hassle just because it's a sole consumer.
--
Pavel Begunkov
next prev parent reply other threads:[~2024-05-08 15:44 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
2024-05-08 14:25 ` Jason Gunthorpe
2024-05-08 15:44 ` Pavel Begunkov [this message]
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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