Hi Madalin, > > > Thanks a lot for the info, will look into this. Do you have any > > > pointers as to why the full page restriction exists in the first > > > place? Sorry if it's a dumb question, but I haven't found details on > > > this and I'd really like to understand it. > > > > Hi Ioana, > > > > I promised (offlist) that I would get back to you explaining the XDP > > page-requirement... > > > > There are several reasons for XDP to require frames are backed by a > > page. It started out with a focus on gaining speed via simplicity. > > > > The overall requirement is: XDP frame in physical contigious memory > > - which is a requirement from BPF Direct-Access, for validating > > correcness. > > - Implying you cannot split packet data over several pages. > > > > An important part of the page-requirement is to allow creating SKB's > > outside the driver code. This happen today in both cpumap and veth > > (when doing XDP_REDIRECT). And we need to control and limit the > > variations, to avoid having to handle all kind of SKB schemes. > > Specifically we need enough tailroom for the skb-shared-info. > > > > In the beginning we had the requirement of: 1-page per XDP frame. > > - Gave us a simplified memory model > > - Allow us to not touch atomic refcnt on page (always 1) > > - Fixed 256 bytes headroom > > - This gave us a lot of tailroom, expanding tail was trivial. > > > > Eventually ixgbe+i40e force us to use a split-page model, allowing two > > frames per page. > > - This started to complicate memory model > > - This unfortunately gave issue of unknown tailroom, which killed the > > tailroom expand option. > > - Changes XDP headroom to be variable (192 or 256 bytes) > > Hi Jesper, > > is the split page memory model supported now (with two frames per page)?
Yes, both Intel on their ixgbe and i40e driver and mellanox on mlx5 support this. Cheers /Ilias
