linux-kernel - Re: [RFC PATCH net-next v6 02/15] net: page_pool: create hooks for custom page providers

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Date: Tue, 26 Mar 2024 13:19:20 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Christoph Hellwig <hch@...radead.org>, shakeel.butt@...ux.dev
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-alpha@...r.kernel.org, 
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	linux-kselftest@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jonathan Corbet <corbet@....net>, Richard Henderson <richard.henderson@...aro.org>, 
	Ivan Kokshaysky <ink@...assic.park.msu.ru>, Matt Turner <mattst88@...il.com>, 
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	Pavel Begunkov <asml.silence@...il.com>, David Wei <dw@...idwei.uk>, Jason Gunthorpe <jgg@...pe.ca>, 
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	Harshitha Ramamurthy <hramamurthy@...gle.com>, Jeroen de Borst <jeroendb@...gle.com>, 
	Praveen Kaligineedi <pkaligineedi@...gle.com>
Subject: Re: [RFC PATCH net-next v6 02/15] net: page_pool: create hooks for
 custom page providers

On Sun, Mar 24, 2024 at 4:37 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Fri, Mar 22, 2024 at 10:54:54AM -0700, Mina Almasry wrote:
> > Sorry I don't mean to argue but as David mentioned, there are some
> > plans in the works and ones not in the works to extend this to other
> > memory types. David mentioned io_uring & Jakub's huge page use cases
> > which may want to re-use this design. I have an additional one in
> > mind, which is extending devmem TCP for storage devices. Currently
> > storage devices do not support dmabuf and my understanding is that
> > it's very hard to do so, and NVMe uses pci_p2pdma instead. I wonder if
> > it's possible to extend devmem TCP in the future to support pci_p2pdma
> > to support nvme devices in the future.
>
> The block layer needs to suppotr dmabuf for this kind of I/O.
> Any special netdev to block side channel will be NAKed before you can
> even send it out.

Thanks, a few questions if you have time to help me understand the
potential of extending this to storage devices.

Are you envisioning that dmabuf support would be added to the block
layer (which I understand is part of the VFS and not driver specific),
or as part of the specific storage driver (like nvme for example)? If
we can add dmabuf support to the block layer itself that sounds
awesome. We may then be able to do devmem TCP on all/most storage
devices without having to modify each individual driver.

In your estimation, is adding dmabuf support to the block layer
something technically feasible & acceptable upstream? I notice you
suggested it so I'm guessing yes to both, but I thought I'd confirm.

Worthy of note this is all pertaining to potential follow up use
cases, nothing in this particular proposal is trying to do any of this
yet.

-- 
Thanks,
Mina