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

From: David Wei <dw@davidwei.uk>
To: Christoph Hellwig <hch@infradead.org>,
	Mina Almasry <almasrymina@google.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-alpha@vger.kernel.org,
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	dri-devel@lists.freedesktop.org,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
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	"Helge Deller" <deller@gmx.de>,
	"Andreas Larsson" <andreas@gaisler.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
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	"Christian König" <christian.koenig@amd.com>,
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	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Yunsheng Lin" <linyunsheng@huawei.com>,
	"Shailend Chand" <shailend@google.com>,
	"Harshitha Ramamurthy" <hramamurthy@google.com>,
	"Jeroen de Borst" <jeroendb@google.com>,
	"Praveen Kaligineedi" <pkaligineedi@google.com>
Subject: Re: [RFC PATCH net-next v6 02/15] net: page_pool: create hooks for custom page providers
Date: Sun, 17 Mar 2024 19:49:43 -0700	[thread overview]
Message-ID: <b938514c-61cc-41e6-b592-1003b8deccae@davidwei.uk> (raw)
In-Reply-To: <ZfegzB341oNc_Ocz@infradead.org>

On 2024-03-17 19:02, Christoph Hellwig wrote:
> On Mon, Mar 04, 2024 at 06:01:37PM -0800, Mina Almasry wrote:
>> From: Jakub Kicinski <kuba@kernel.org>
>>
>> The page providers which try to reuse the same pages will
>> need to hold onto the ref, even if page gets released from
>> the pool - as in releasing the page from the pp just transfers
>> the "ownership" reference from pp to the provider, and provider
>> will wait for other references to be gone before feeding this
>> page back into the pool.
> 
> The word hook always rings a giant warning bell for me, and looking into
> this series I am concerned indeed.
> 
> The only provider provided here is the dma-buf one, and that basically
> is the only sensible one for the documented design.  So instead of
> adding hooks that random proprietary crap can hook into, why not hard
> code the dma buf provide and just use a flag?  That'll also avoid
> expensive indirect calls.

I'm working on a similar proposal for zero copy Rx but to host memory
and depend on this memory provider API.

Jakub also designed this API for hugepages too IIRC. Basically there's
going to be at least three fancy ways of providing pages (one of which
isn't actually pages, hence the merged netmem_t series) to drivers.

> 