On Mon, Mar 18, 2002 at 07:13:19AM -0800, John Clark wrote:

 > Well, where I tuned into this was hand tracing recv()/send() network
 > operations, or then use of the 'pipe' to transfer data. In either case,
 > there's a 'uiomove' which uses copyin/out. Now for the 'strange' thing,
 > there's a chunk of code in 'sys_pipe' which has a #define __FreeBSD__
 > which appears to map pages from the sender to the receiver without
 > any copy of the actual data at all...

Actually, there is a NetBSD version of that code, as well, and in -current,
the page-flipping code is enabled for pipes by default.

Those particular optimizations are pipe-specific, though, making assumptions
about how data flows on pipes.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>