linux-kernel - Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for custom page providers

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Message-ID: <8f44ca2a-8910-418f-b4a6-ca1e051484ba@gmail.com>
Date: Fri, 7 Jun 2024 16:42:43 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: David Ahern <dsahern@...nel.org>, Mina Almasry <almasrymina@...gle.com>
Cc: Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org,
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Subject: Re: [PATCH net-next v10 02/14] net: page_pool: create hooks for
 custom page providers

On 6/7/24 15:27, David Ahern wrote:
> On 6/7/24 7:42 AM, Pavel Begunkov wrote:
>> I haven't seen any arguments against from the (net) maintainers so
>> far. Nor I see any objection against callbacks from them (considering
>> that either option adds an if).
> 
> I have said before I do not understand why the dmabuf paradigm is not
> sufficient for both device memory and host memory. A less than ideal
> control path to put hostmem in a dmabuf wrapper vs extra checks and
> changes in the datapath. The former should always be preferred.

If we're talking about types of memory specifically, I'm not strictly
against wrapping into dmabuf in kernel, but that just doesn't give
anything.
But the main reason for allocations there is the difference in
approaches to the api. With io_uring the allocation callback is
responsible for getting buffers back from the user (via a shared
ring). No locking for the ring, and buffers are already in the
context (napi) where they would be consumed from. Removes some
headaches for the user (like batching before returning buffers),
and should go better with smaller buffers and such.

> I also do not understand why the ifq cache 

I'm not sure what you mean by ifq cache. Can you elaborate?

> and overloading xdp functions

Assuming it's about setup via xdp, it was marked for remaking in
RFCs for longer than desired but it's gone now in our tree (but
maybe not in the latest series).

> have stuck around; I always thought both were added by Jonathan to
> simplify kernel ports during early POC days.

-- 
Pavel Begunkov