Freemem on 3B1

[was-John McMillan]

In article <1989Nov7.223023.14300 at alberta.uucp> dutchyn at alberta.uucp (Chris Dutchyn) writes:
> :
>	I have 3.5 Mb or RAM, at boot up, I have 3.3M left after
>the initial kernel, I then have 200K of loaded device drivers (according
>to lddrv -s).  Then, according to SZ and RSZ from ps, I have approximately
>200K of background processes, login/gettys ...  Therefore, it would
>appear that I should have:
>		3300 - 200 - 200 = 2900K
>left for user processes.  Yet, I never see the sysinfo line say more than
>2.36 MB memory.

	A reasonable mis-impression.  Let's look closer, tho':
		450K	-- The real kernel size.
			150K	-- TEXT + Compiled DATA&BSS
			250K	-- TUNABLES, alloc'd arrays, Stacks
			 50K	-- (Pageable) Screen-maps, etc.
		150K	-- Shared Library TXT + 1*DATA (init's copy, Pageable)

		200K	-- wmgr+lpsched+rasdaemo+smgr (Pageable)
		200K	-- ph (1/2 paged out under low demand)

		200K	-- Loadables
		----
		1200K	-- approx load w/o any user programs.

>	Next, I never see the sysinfo line go below 0.79 MB memory.  As soon
>as it hits about 0.80 MB, I can head the hard drive start to grind as if
>it needs to swap/page.  But, above that, I only hear ordinary file accesses.
>Does this mean that I wasted the last 0.5 M I installed in may machine? 

	How slowly do you want processes to start up?  If 100% of
	RAM is 'in use' then you cannot acquire ONE page without
	forcing another out.  One facet of the paging strategy involves
	moving out infrequently used pages to assure IMMEDIATE
	availability of pages for program star-ups and for growths
	(stack increases & mallocs).  If you're running a heavily
	loaded system that figure should drop -- until the load
	eases up: you didn't waste the RAM!  (PS: I faintly recall
	that it's 20% of RAM it tries to keep free.)

>				Christopher Dutchyn
>	University of Alberta	dutchyn at cs.alberta.can
>	Edmonton, AB		       !alberta!watmath!uunet...

john mcmillan	-- att!mtunb!jcm -- just muttering for self, not THEM