On 2023/8/17 1:01, Ilias Apalodimas wrote: > 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? I used the key in the original report: https://www.spinics.net/lists/netdev/msg779890.html >> Please see the bisection report below about a boot failure on >> rk3288-rock2-square which is pointing to this patch. The issue >> appears to only happen with CONFIG_ARM_LPAE=y. grepping the 'CONFIG_PHYS_ADDR_T_64BIT' seems to be more common? https://elixir.free-electrons.com/linux/v6.4-rc6/K/ident/CONFIG_PHYS_ADDR_T_64BIT > >> >>> >>>> >>>> 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 Did you mean a xdp frame containing a frag page can not be passed to the xdp core? What is exact reason why the XDP verifier need a packet per page? Is there a code block that you can point me to? I wonder if it is still the case for now, as bnxt and mlx5 seems to be supporting frag page and xdp now. > 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 >>> > . >
