Coalescing pipe allocation

[Matthew Dillon]

:...
:Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
:robert at fledge.watson.org      Senior Research Scientist, McAfee Research

    It seems to me that realizing the lion's share of the benefit requires 
    only that you cache the KVM reservation for a pipe buffer, and that
    you perhaps separately cache pipe meta data structures.  I think
    you would only get a smidgen more performance by caching the entire
    pipe pair, so it seems a bit overkill to do that.  By my quick read it
    looks like it would be trivial to create a small per-cpu (UMA based for
    you guys, globaldata based for me) cache.  A hysteresis of 4 ought to
    be sufficient.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>