On 2023/8/16 19:26, Ilias Apalodimas wrote:

Hi Yunsheng

On Mon, 14 Aug 2023 at 15:59, Yunsheng Lin [off-list ref] wrote:

quoted

Currently page_pool_alloc_frag() is not supported in 32-bit
arch with 64-bit DMA because of the overlap issue between
pp_frag_count and dma_addr_upper in 'struct page' for those
arches, which seems to be quite common, see [1], which means
driver may need to handle it when using frag API.

That wasn't so common. IIRC it was a single TI platform that was breaking?

I am not so sure about that as grepping 'ARM_LPAE' has a long
list for that.

quoted

In order to simplify the driver's work when using frag API
this patch allows page_pool_alloc_frag() to call
page_pool_alloc_pages() to return pages for those arches.

Do we have any use cases of people needing this?  Those architectures
should be long dead and although we have to support them in the
kernel,  I don't personally see the advantage of adjusting the API to
do that.  Right now we have a very clear separation between allocating
pages or fragments.   Why should we hide a page allocation under a
frag allocation?  A driver writer can simply allocate pages for those
boards.  Am I the only one not seeing a clean win here?

It is also a part of removing the per page_pool PP_FLAG_PAGE_FRAG flag
in this patchset.

Thanks
/Ilias