AIX

Hi ,

I have 8Gb memory in my JS21 server. When I run svmon it shows 3655Mb memory is utilized and 4344Mb free. I have configured 8Gb paging space and 14% is utilized which is 1Gb. I dont have memory issues but just want to know Why 1gb paging is utilized when my almost 4Gb real memory is free? Can anyone give some input...

Hi,
several possible reasons - is this AIX 5.3 ? If so - what are the values of minperm, maxperm and lru_file_repage ? Is your box running DBs or webapplications ?

Regards
zxmaus

Is it still true that AIX will always page out? Even when there is no memory shortage? I recall from AIX 4 days that AIX would always page out "less import" memory pages even if the system had enough free memory.

No. I suppose this is the background of zxmaus asking which OS-version you are running in this box.

Still, without answering her questions it is quite impossible to answer yours, so you might consider answering them.

bakunin

@petervg:
No, it should only page out when there is RAM shortage these days. There is an early and late/deferred Paging Space allocation mode, that you can export with some env variable to control OS/applications behaviour in terms of Paging Space usage.

@vjm:
As zxmaus said, several reasons. It might be also interessting to have 24/7 monitoring of Paging Space up and running, like a

Code:

nohup vmstat -wtI 2 & >> /somedir/vmstat.log 2>&1

It could be, that the box is not paging at all on day time when you can have a glimpse on it, but at night while running backups or batch jobs etc., it might occure.

When this line above runs for some days, you could check (choose a filesystem for the log that has enough space and isn't critical!) it, if there is any Paging Space Ins or Outs occuring with:

Code:

awk '/kthr/ && !h {print; getline; print; h=1} $1 ~ /^[0-9]+$/ && ( $8 != 0 || $9 != 0 )' vmstat.log

which would produce the following (example) output:

Code:

   kthr            memory                         page                       faults                 cpu             time
----------- --------------------- ------------------------------------ ------------------ ----------------------- --------
  2   0   0     245267      31399     0     1     20     0     0      0    32    852   449  3  3 93  0  0.02   9.5 12:27:32
  6   0   0     245267      31399     0     0     0      8     0      0    30    454   384  1  2 97  0  0.01   5.4 12:27:44
  1   0   0     245459      31204     0     0     22     0     0      0    30    659   416  1  3 96  0  0.01   6.9 12:28:10

@zxmaus

oslevel is 5300-07-01-0748

minperm%6 = 20
maxperm% = 80
lru_file_repage = 1

my box is running sybase.

Thank you ...

Try following settings:

vmo -p -o minperm%=3
vmo -p -o maxperm%=90
vmo -p -o lru_file_repage=0

and reboot. I am pretty sure your paging space utilization will stop afterwards.

Regards
zxmaus