On Sun, May 22, 2022 at 07:04:36PM +0000, Al Viro wrote:
> copy_page_{from,to}_iter() iovec side is needed not for the sake of
> optimizations - if you look at the generic variant, you'll see that it's
> basically "kmap_local_page + copy_{to,from}_iter() for the contents +
> kunmap_local_page", which obviously relies upon the copy_{to,from}_iter()
> being non-blocking. So iovec part of it genuinely needs to differ from
> the generic variant; it's just that on top of that it had been (badly)
> microoptimized. So were iterators, but that got at least somewhat cleaned
> up a while ago. And no, turning that into indirect calls ended up with
> arseloads of overhead, more's the pity...
Actually, I take that back - the depth of kmap stack won't be increased
by more than one compared to mainline, so we can switch iovec and ubuf
variants to generic.
See #new.iov_iter; I do like the diffstat - -110 lines of code, with new
flavour added...
Completely untested, though.
