Comment by BeeOnRope

Thanks, you mention explicitly kernel networking right below about the send path:

> before flinging them at the kernel as [vectors of] large, contiguous DMA requests, without having to stop to allocate

So I had assumed you were taking about kernel networking elsewhere as well.

BTW, on the kernel send path, there is again a copy, contiguous or not, regardless of what API you use.

When using kernel networking I don't think contiguity matters as you suggest, as there is always a copy. Furthermore "contiguous" in userspace doesn't correspond to contiguous in physical address space so in any case the hardware is just often going to see a userspace buffer as a series of discontiguous pages anyway: that's what happens with direct IO disk writes, which _are_ zero copy (huge pages helps).