Write caching on FreeBSD

[jdy at jdyson.com]

Quick comment:

	When doing/updating the write code, I carefully
	limited the amount of pending write data so that
	the system wouldn't 'go to sleep' while trying
	to sync out massive amounts of data.  For convienience,
	this amount of write space was limited by the disk
	cache buffer representation.  My original disk cache
	code wasn't limited to the cache buffers, and would	
	actually create large numbers of dirty pages.  This
	allowed for faster performance, except under load.

	I was interested in the high load performance conditions,
	and some mods have apparently been made to support
	more pending writes (by increasing the disk buffer
	cache representations?)  Anyway, it seems like FreeBSD
	currently has a good compromise (better than my original,
	but also better than a no-holds barred scheme that
	creates lots of dirty pages.)

	John