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 direction to be moving for co-existence. Adding fake struct page instances is the wrong direction.
