AIX

Hi,

We have AIX 5.1 machine of RAM 8 GB and paging space is 8GB. we are getting high memory usage of almost 99%.Can anybody please help in this ?

Partial vmstat o/p

kthr memory
----- -----------
r b avm fre
2 1 278727 1143

There is no paging issue.Becoz in vmstat output pi and po are always 0Should we need to increase the AVM (active virtual memory) or how to resolve this.


Regards,
Jayakumar

Jayakumar,

AIX is trying to get the most out of your memory, it is using the available memory as file cache. This to prevent reading from the 'slow' disks and thereby speeding up the system. When there is no paging then there is no reason to worry. If you want (and really, really want) to influence this behavior you can fiddle with the famous minperm/maxperm parameters..

If you look in this forum for the string "aix memory breakdown" you might find more info about this subject, "pagink" included a link that might give you a more in depth answer.

Seems you have nothing to wory about there mate.
As rvegmond said AIX just uses memory like that.
If it isn't paging then there is nothing to worry about, AIX is just using the available physical memory to cache filesystem instead of keep waiting to write it in and out of disk space.

Thanks for the reply.One thing i am wondering.Sometime back the server was having 4GB ram and recently upgraded to 8 GB.Before upgrading from 4 to 8 GB RAM it was showing 99% memory usage & after upgradation also the same case..

Can anybody throw light on this. ?

If you have the output of "vmstat" from before the upgrade ready have a look at it: i bet you will see a lot of swapping going on and probably now you won't see any (or at least much less than before). The same is perhaps true for the output of "lsps -a", which tells you about the utilization of the swapspaces: perhaps the numbers decreased steeply after upgrading the RAM.

UNIX tries to use the RAM given to it as efficiently as possible: First all the processes started get the memory they need. Some memory is set aside for network buffers, file cache, etc. If still memory is available these buffers will increase in size - which buffers increases how much depends on how the machine is used: more disk-I/O, more network traffic, etc.. The administrator can tune the kernel built-in heuristics with the tools vmo (virtual memory options), schedo (scheduler options), no (network options) and ioo (I/O-options). See the manpages of these tools and the documentation of /etc/tunables for more information.

If no memory is available after satisfying the started processes demands paging occurs: memory pages are taken from the "computational memory" (memory occupied by programs by swapping them out to the paging space) or from the "file memory" (the file cache). When and how much is taken from what can also be tuned, see the "maxperm" and "minperm" parameters in "vmo".

Of course i cannot give you a detailed documentation of the AIX kernel here: what i wrote above are only glimpses and pretty unsorted ones. If you are interested in the details there are two IBM classes (AIX System Administration III: Performance Tuning; AIX Kernel Internals; each 5 days). There are also Redbooks (IBM Redbooks | AIX 5L Practical Performance Tools and Tuning Guide, IBM Redbooks | AIX 5L Performance Tools Handbook, IBM Redbooks | Database Performance Tuning on AIX) available, read them for further details.

I hope this helps.

bakunin

As said above:

"Seems you have nothing to wory about there mate.
As rvegmond said AIX just uses memory like that.
If it isn't paging then there is nothing to worry about, AIX is just using the available physical memory to cache filesystem instead of keep waiting to write it in and out of disk space."

If you give (gave) AIX more memory, it will just cache more to save disk I/O, as long as there is no paging and the memory is fully utilised (which it should be in a well tuned active system) you have nothing to worry about.