AIX 5L default memory usage..comments please!

[polani]

Dear wise users of group..
I want to have some comments on AIX 5.2 default memory usage
structure... i have seen that by default, AIX 5.2 uses more than 50%
of real memory for file caching while remaining real memory ( like
30-40% ) is used for user applications....
If this my observation is correct then why it is so b/c in most of
the cases even not running any db or applications on AIX 5L servers ,
svmon or Nmon reports 100% memory utilization .....Then off course
while db is running system starts paging..
My question is that:

vmo command should be used with what parameters to change this default behavior!!!!
what are you users recommended settings with which to start
???


Here comes polani Once again!!!

P690 Certified Specailist
HACMP & AIX Certified Specailist
AIX & HACCMP Instructor

 

[Ogzilal]

Hi Polani,

to know exactly what % of RAM is used for buffer files in your system, just type the following commands :

vmo -L minperm
The display will look like this
NAME CUR DEF BOOT MIN MAX UNIT TYPE
DEPENDENCIES
--------------------------------------------------------------------------------
minperm 200426 200426 S
--------------------------------------------------------------------------------

200426 is the minimum number of 4K pages reserved for buffer files in RAM (about 10% of my 8388608 Kbyte RAM )

To know the max % used for buffer files :

vmo -L maxperm

NAME CUR DEF BOOT MIN MAX UNIT TYPE
DEPENDENCIES
--------------------------------------------------------------------------------
maxperm 1565K 1565K S
--------------------------------------------------------------------------------

1565K is the max number of 4Kbyte pages reserved for buffer files.

Another important parameter to know about is strict_maxperm :
vmo -L strict_maxperm

NAME CUR DEF BOOT MIN MAX UNIT TYPE
DEPENDENCIES
--------------------------------------------------------------------------------
strict_maxperm 1 0 1 0 1 boolean D
--------------------------------------------------------------------------------

Explanation : strict_maxperm is a boolean, when set to false (0), it tells the system to use more than maxperm parameter if needed, this way 100% of RAM will be used for buffer files, this lead to system crash in some situations.
when this parameter is set to true (1) maxperm % of RAM will never be overpassed, buffer files in memory will be flushed out to disk evrytime they reach maxperm pages.

To change this parameters, commands will be like :

changing minperm : vmo -p -o minperm%=20
changing maxperm : vmo -p -o maxperm%=60
changing strict_maxperm : vmo -p -o strict_maxperm=1

minperm and maxperm are Static, the changes will take effect in next boot.

strict_maxperm is dynamic, the change takes effect immediatly.

man vmo for more deatails on other tunable parameters.

Ali