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

[Yunsheng Lin]

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
> .
>