How do I know swap usage is high or low?

[Rashid Ali]

# swapinfo -tm
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 704 54 650 8% 0 - 1 /dev/vg00/lvol2
dev 220 56 164 25% 0 - 1 /dev/vg00/lvol4
reserve - 650 -650
memory 765 479 286 63%
total 1689 1239 450 73% - 0 -
# bc
sc=2
1239/1689
.73
#
Inside GlancePlus, I keyed in 'w' to see swap usage as below,

Swap Available: 1689mb Swap Used: 588mb Swap Util (%): 73 Reserved: 1238mb
Type 'm' to see memory usage as below,

Total VM : 427.2mb Sys Mem : 82.3mb User Mem: 457.4mb Phys Mem: 1024mb
Active VM: 127.3mb Buf Cache: 462.3mb Free Mem: 21.9mb

How come I got swap used is 588mb from GlancePlus and got 479mb from swapinfo?
How do I know swap usage is high or low?
Higher than 60% or 70% considered high?
Should I increase swap space to lower down swap usage? But it seems not true, because the swap used in two device swaps and not much.

Thanks in advance,

[Rashid Ali]

I got it. It is because swap used =54+56+479=589MB. But what is memory paging and which parameter can enable it? Is it swapmem_on? But the description says it indicates "Allow Memory to Exceed Swap Space" when swapmem_on=1, what does it mean? Also, the command swapon is fired in /sbin/init.d/swap_start to enable swap space.

[Carsten Krege]

If swapmem_on=1 is set you enabled pseudo-swap. This is a concept that allows you not to do active swap space allocation if you have at least 25% of your memory unused (if you have still free memory, you won't starting paging anyway thus making swap space allocation unnecessary). HPUX handles pseudo-swap as if you have allocated the swap space in memory, but in fact you really don't allocate any swap space (neither in memory nor on disk).

A good description of the concept is in the Memory Management White Paper in /usr/share/doc/mem_mgt.txt (search for "Pseudo-Swap Space").

Carsten

[RAJESH GANGADHARAN]

if swapmem_on =1 it will use the free memory for paging
insted of paging to disk

[Rashid Ali]

So if my memory usage is very high, always more than 98%. Should I set swapmem_on=0 ?