🚀 go-pugleaf

In article <PCG.89Sep2220027@thor.cs.aber.ac.uk> pcg@thor.cs.aber.ac.uk
(Piercarlo Grandi) writes:
>The BSD pager was designed very very well by an extremely
>competent person with a specialization in performance analysis of
>virtual memory; unfortunately it was developed on a machine with
>512Kbytes. On today's machines with 8-16-32 Mbytes, a clock scan
>may take several minutes, making the well designed algorithm
>essentially useless. A good example of how unanticipated changes
>of scale make algorithms inappropriate.

It was retuned fairly early for a 2 MB machine (probably ernie or
ucbvax), and the 2 MB version is what was in 4.1 and 4.2 BSD.  Since
then it has been redone as a two-handed clock (one for simulating
reference, one for freeing pages) and the hands set 2 MB apart.  That
helps a great deal, but the system still does not really deal well with
heavy paging loads, mostly because DEC disks are too slow.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris