On Wed, 16 Aug 2023 at 15:49, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: > > On 2023/8/16 19:26, Ilias Apalodimas wrote: > > Hi Yunsheng > > > > On Mon, 14 Aug 2023 at 15:59, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote: > >> > >> 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. Shouldn't we be grepping for CONFIG_ARCH_DMA_ADDR_T_64BIT and PHYS_ADDR_T_64BIT to find the affected platforms? Why LPAE? > > > > >> > >> 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. Yes, that happens *because* of this patchset. I am not against the change. In fact, I'll have a closer look tomorrow. I am just trying to figure out if we really need it. When the recycling patches were introduced into page pool we had a very specific reason. Due to the XDP verifier we *had* to allocate a packet per page. That was expensive so we added the recycling capabilities to compensate and get some performance back. Eventually we added page fragments and had a very clear separation on the API. Regards /Ilias > > > > > Thanks > > /Ilias > >
