Why does memory go down in vmstat

[Tison]

Why does the free mem go down in vmstat ?
kthr memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 1 46283 193717 0 0 0 0 0 0 298 1035 218 3 4 71 22
0 2 46284 193713 0 0 0 0 0 0 367 1387 319 0 1 94 4
0 2 46284 193712 0 0 0 0 0 0 357 379 303 0 0 99 0
0 2 46284 193712 0 0 0 0 0 0 358 401 304 0 0 99 0
0 2 46284 193712 0 0 0 0 0 0 360 367 302 0 1 99 0
System 1 hour later
kthr memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 1 197304 41027 0 0 0 0 0 0 465 1724 427 15 3 55 27
0 2 197305 41025 0 0 0 0 0 0 354 1320 304 0 1 99 0
0 2 197305 41025 0 0 0 0 0 0 358 383 301 0 0 99 0
0 2 197305 41025 0 0 0 0 0 0 358 374 303 0 0 99 0
0 2 197305 41025 0 0 0 0 0 0 356 382 302 0 1 99 0

 

[MoshiachNow]

Normally,

It's because the system needs it for the application you are running.

It may go down to the limit defined by vmtune params.
See

http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg246184.pdf

Chapter 3.

"Long live king Moshiach !"

http://www.7for70.com/

 

[letis]

Hello Tison,

it's an AIX 'perticularity', ie it will try to maximise the use of physical memory.

For information, by default, AIX will considet that it has the right to use from 20 up to 80% of the RAM for filesystem cache purpose. Thus, the first time that for example you copy a file from a location to another, the file will automatically be cached in RAM (and access time will be much higher at the second copy).

This can have unwanted effect such paging (not the case in the sample you submitted) check the redbook recommanded by levw !

regards,