On 2023/11/16 23:58, David Ahern wrote: > On 11/16/23 4:12 AM, Yunsheng Lin wrote: >> On 2023/11/16 1:57, David Ahern wrote: >>> On 11/15/23 2:21 AM, Yunsheng Lin wrote: >>>> On 2023/11/14 21:16, Jason Gunthorpe wrote: >>>>> On Tue, Nov 14, 2023 at 04:21:26AM -0800, Mina Almasry wrote: >>>>> >>>>>> Actually because you put the 'strtuct page for devmem' in >>>>>> skb->bv_frag, the net stack will grab the 'struct page' for devmem >>>>>> using skb_frag_page() then call things like page_address(), kmap, >>>>>> get_page, put_page, etc, etc, etc. >>>>> >>>>> Yikes, please no. If net has its own struct page look alike it has to >>>>> stay entirely inside net. A non-mm owned struct page should not be >>>>> passed into mm calls. It is just way too hacky to be seriously >>>>> considered :( >>>> >>>> Yes, that is something this patchset is trying to do, defining its own >>>> struct page look alike for page pool to support devmem. >>>> >>> >>> Networking needs to be able to move away from struct page references. >>> The devmem and host memory for Rx use cases do not need to be page based. >> >> Yes, I am agreed the ultimate goal is to move away from struct page >> references. But I am not sure if we can do it right away as there >> still are different types of existing 'struct page' in the netstack, >> see: >> >> https://lore.kernel.org/all/8b7d25eb-1f10-3e37-8753-92b42da3fb34@xxxxxxxxxx/ > > yes, that is the point of a blended approach -- pages and buffers (or > iov) -- leveraging the LSB of the address. That proposal is the right I am not sure leveraging the LSB of the address is necessary yet, as it does not seems to provide the type check protection, it seems to just provide a way to demux between pages(including page pool owned page and non-page pool owned page) and page pool owned buffer. That info is avaliable through the page->pp_magic and page->pp->mp_* too if we mirror the page pool specific union in 'struct page'. > direction to be moving for co-existence. Adding fake struct page > instances is the wrong direction. Perhaps a fake struct page with type check protection is the right direction? Intergrating devmem to page pool without a unified metadata between pages and buffers or without a proper abstract layer does not seems like the good direction either. > . >
