On 17-01-24 01:56 PM, Michael S. Tsirkin wrote: > On Tue, Jan 24, 2017 at 04:10:46PM -0500, David Miller wrote: >> This works in the regimen that XDP packets always live in exactly one >> page. That will be needed to mmap the RX ring into userspace, and it >> helps make adjust_header trivial as well.
I still don't see why this is a hard requirement for mmap let me post some patches later tonight to show how we do this with af_packet. > > I think the point was to avoid resets across xdp attach/detach. If we > are doing resets now, we could do whatever buffering we want. We could > also just disable mergeable buffers for that matter. > >> MTU 1500, PAGESIZE >= 4096, so a headroom of 256 is no problem, and >> we still have enough tailroom for skb_shared_info should we wrap >> the buffer into a real SKB and push it into the stack. >> >> If you are trying to do buffering differently for virtio_net, well... >> that's a self inflicted wound as far as I can tell. > > Right but I was wondering about the fact that this makes XDP_PASS > much slower than processing skbs without XDP, as truesize is huge > so we'll quickly run out of rmem space. > > When XDP is used to fight DOS attacks, why isn't this a concern? > It is a concern on my side. I want XDP and Linux stack to work reasonably well together. .John
