mathematics of swap space

[Bill Wohler]

swap space gurus:

  with 128M of real memory and 208M of swap (and effective total of
  336M of memory!) on a 530, i would not have expected to see "INIT:
  swap space low", especially considering when the sum of the SIZE
  column of "ps uax" is only 58M.

	ps uax | awk '{sum += $5}
	END {print sum}'
	57876

  researching this problem via info revealed the following numbers:

[wohler at aix3:175]% lsps -a 
Page Space  Physical Volume   Volume Group    Size   %Used  Active Auto
paging00    hdisk1            uservg          64MB      65     yes yes
hd6         hdisk0            rootvg         144MB      34     yes yes
					     ---
					     208

[root at aix3:201]# vmstat
procs    memory             page              faults        cpu     
----- ----------- ------------------------ ------------ -----------
 r  b   avm   fre  re  pi  po  fr   sr  cy  in   sy  cs us sy id wa 
 1  0 24401 11756   0   0   0   0    2   0 117   55  37  1  1 96  0


24401 (avm) * 4096 = 96604k

11756 (fre) * 4096 = 47024k
	           --------
                    144628k

  these numbers and info raise the following questions which info
  couldn't answer.  i'd be very thankful for any of your answers:

	o what percentage of paging space free is considered to be a
	  low condition (ie. SIGDANGER's sent to processes)?

	o is the total amount of available virtual space just the swap space,
	  or real memory plus swap space?

	o what program is used to determine how much real memory the
	  system thinks it has?

	o why is the swapper process so large?

	o why is the total amount of available and free memory
	  displayed by vmstat not equal to 208 displayed by lsps?

	o why is there such a discrepancy between the sum of the SIZE column
	  of ps and the avm field of vmstat?

  in summary,  do these numbers indicate a bug or a broken
  configuration?  why did the system indicate that we ran out of swap
  space?  what other tools do we have at our disposal?
-- 
						--bw
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Bill Wohler <wohler at sap-ag.de> <sapwdf!wohler>
Heidelberg Red Barons Ultimate Frisbee Team