this problem with this approach is that it unbalances the system
	too much in favor of anonymous data.  if there is enough swap-backed
	data to fill the 2/3 of memory which we attempt to keep in the active queue,
	then vnodes will only have the 1/3 of memory in the inactive queue available
	to cache their data, which is silly if the anonymous memory is (eg.)
	netscape's in-memory cache and netscape has been iconified in the corner
	of the screen all day while the user has been trying to do some file-
	intensive work.

Chuck, that is precisely the behavor everyone is complaining
about.  If you're running with a high I/O load that means you
are working your way through pages at a high rate.  Both the 
X server and X applications tend to be bursty in both CPU useage 
and page useage since they execute based on user input.  If
you're writing a document and stop to think for 20 seconds
YOU DO NOT WANT YOUR X SERVER AND EDITOR SWAPPED OUT, which
is what happens right now, even with all of the page scanner
fixes.  

Sacrificing a few dozen pages of buffer cache for an 
iconified in-memory netscape is precisely the trade you want
to make on an interactive system.  The reason you iconify a
program rather than terminate it so it gives up all its
resources is that you want it to be instantly accessible.
Being forced to page it all in is precisely what you don't
want.

	I do agree that the paging algorithm does need to be enhanced,
	but this isn't the way to do it.    from subsequent mail on this list,
	it appears that people are already figuring out that part of the problem
	is a simple error on my part, but I haven't ready through all the rest
	of this week's tech-kern mail yet, so I'm not sure where things stand
	right now.

Priority  paging and buffer cache high water marks do the
same thing as putting UBC pages directly on the inactive
list, but are more complex and less adaptive.

	-Chuck



	On Tue, Jan 23, 2001 at 07:34:10PM -0000, eeh@netbsd.org wrote:
	> 
	> Here's a little fix I threw together to improve the performance of
	> UBC under I/O load.  What it does is put buffer cache pages on the
	> uvm inactive list when an IOP completes instead of leaving them on
	> the active list for the page scanner to reclaim.  This has several
	> effects:  it makes buffer cache pages more likely to be reclaimed
	> than other pages, and it slightly reduces the load on the pagedaemon.
	> 
	> Eduardo