netdev - Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

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Message-ID: <0a1cdd5a-c4c5-3d77-20a2-2beb8e3a6411@huawei.com>
Date: Thu, 16 Nov 2023 19:10:01 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Mina Almasry <almasrymina@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
	<davem@...emloft.net>, <pabeni@...hat.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Willem de Bruijn <willemb@...gle.com>,
	Kaiyuan Zhang <kaiyuanz@...gle.com>, Jesper Dangaard Brouer
	<hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, Eric
 Dumazet <edumazet@...gle.com>, Christian König
	<christian.koenig@....com>, Matthew Wilcox <willy@...radead.org>, Linux-MM
	<linux-mm@...ck.org>
Subject: Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

On 2023/11/15 21:38, Jason Gunthorpe wrote:
> On Wed, Nov 15, 2023 at 05:21:02PM +0800, Yunsheng Lin wrote:
> 
>>>>> I would expect net stack, page pool, driver still see the 'struct page',
>>>>> only memory provider see the specific struct for itself, for the above,
>>>>> devmem memory provider sees the 'struct page_pool_iov'.
>>>>>
>>>>> The reason I still expect driver to see the 'struct page' is that driver
>>>>> will still need to support normal memory besides devmem.
>>>
>>> I wouldn't say this approach is unreasonable, but it does have to be
>>> done carefully to isolate the mm. Keeping the struct page in the API
>>> is going to make this very hard.
>>
>> I would expect that most of the isolation is done in page pool, as far as
>> I can see:
> 
> It is the sort of thing that is important enough it should have
> compiler help via types to prove that it is being done
> properly. Otherwise it will be full of mistakes over time.

Yes, agreed.

I have done something similar as willy has done for some of
folio conversion as below:

+#define PAGE_POOL_MATCH(pg, iov)				\
+	static_assert(offsetof(struct page, pg) ==		\
+		      offsetof(struct page_pool_iov, iov))
+PAGE_POOL_MATCH(flags, res0);
+PAGE_POOL_MATCH(pp_magic, pp_magic);
+PAGE_POOL_MATCH(pp, pp);
...

Not sure if we need to add new API for driver to use when the
driver need the devmem support yet.


> 
> Jason
> .
>