On Sat, 11 May 2002, Larry McVoy wrote:
>
> You're only halfway right. You want to avoid the mmap altogether.
See my details on doing the perfect zero-copy copy thing.
The mmap doesn't actually touch the page tables - it ends up being nothing
but a "placeholder".
So if you do
addr = mmap( .. MAP_UNCACHED .. src .. )
mwrite(dst, addr, len);
then you can think of the mmap as just a "cookie" or the "hose" between
the source and the destination.
Does it have to be an mmap? No. But the advantage of the mmap is that you
can use the mmap to modify the stream if you want to, quite transparently.
And it gives the whole thing a whole lot more flexibility, in that if you
generate the data yourself, you'd just do the mwrite() - again with zero
copy overhead.
And I personally believe that "generate the data yourself" is actually a
very common case. A pure pipe between two places is not what a computer is
good at, or what a computer should be used for.
Linus
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Tue May 14 2002 - 12:00:16 EST