Re: [Question] Explanation of zero-copy networking

[Jamie Lokier]

Alan Cox wrote:
> > so there's still single copy for write() of a mmap()ed page?
> 
> An mmap page will go direct to disk.

Looking at the 2.4.4 code, mmap() of file followed by write() to socket
will copy the data once.

I could be mistaken (only glanced at the code quickly) but I base that
on the only call to ->sendpage being through sendfile.

So yes, there's a single copy overhead for mmap()+write().

-- Jamie