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Message-ID: <20231221232343.qogdsoavt7z45dfc@google.com>
Date: Thu, 21 Dec 2023 23:23:43 +0000
From: Shakeel Butt <shakeelb@...gle.com>
To: Mina Almasry <almasrymina@...gle.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kvm@...r.kernel.org,
virtualization@...ts.linux.dev, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella <sgarzare@...hat.com>,
David Howells <dhowells@...hat.com>, Jason Gunthorpe <jgg@...dia.com>,
"Christian König" <christian.koenig@....com>, Yunsheng Lin <linyunsheng@...wei.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next v3 2/3] net: introduce abstraction for network memory
On Wed, Dec 20, 2023 at 01:45:01PM -0800, Mina Almasry wrote:
> Add the netmem_ref type, an abstraction for network memory.
>
> To add support for new memory types to the net stack, we must first
> abstract the current memory type. Currently parts of the net stack
> use struct page directly:
>
> - page_pool
> - drivers
> - skb_frag_t
>
> Originally the plan was to reuse struct page* for the new memory types,
> and to set the LSB on the page* to indicate it's not really a page.
> However, for compiler type checking we need to introduce a new type.
>
> netmem_ref is introduced to abstract the underlying memory type. Currently
> it's a no-op abstraction that is always a struct page underneath. In
> parallel there is an undergoing effort to add support for devmem to the
> net stack:
>
> https://lore.kernel.org/netdev/20231208005250.2910004-1-almasrymina@google.com/
>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>
> ---
>
> v3:
>
> - Modify struct netmem from a union of struct page + new types to an opaque
> netmem_ref type. I went with:
>
> +typedef void *__bitwise netmem_ref;
>
> rather than this that Jakub recommended:
>
> +typedef unsigned long __bitwise netmem_ref;
>
> Because with the latter the compiler issues warnings to cast NULL to
> netmem_ref. I hope that's ok.
>
Can you share what the warning was? You might just need __force
attribute. However you might need this __force a lot. I wonder if you
can just follow struct encoded_page example verbatim here.
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