Paging space page outs when there shouldn't be

[pstupp]

I'm seeing something very strange - on a system with 10GB (don't ask) of free memory, I'm seeing page outs to paging space. Has anyone ever seen this before? Can anyone explain it? I'm trying to piece together a definitive explanation of how the VMM works on AIX v5.2 in the hopes it might explain one of those remote scenarios in which paging can occur even though there is no pressure on memory. For instance, it used to be that on HP-UX, pages read over NFS were paged to paging space so that they don't have to be read over the network again - although, apparently from what I've been reading, this is not the case with AIX. If anyone has any good references on this, or performance as a whole, please let me know.

Thanks

 

[screwloose]

Overcommitted memory.

 

[pstupp]

Could you be more specific? Clearly memory is NOT overcommitted from a system standpoint, there is 10 GB free. Do you mean at a per-process or per-user level?

Thanks

 

[screwloose]

Having too much memory in a machine can cause excessive paging.

 

[Robnhood]

In some cases, you may need to configure the application(s) to use the additional memory.

Progress for example, can be configured to put more of the database in memory.

Craig

http://www.SecurelySpeaking.com

 

[RodKnowlton]

If your working set of computational pages as a percentage of real memory (see topas: % Comp) is less than the VMM "minperm" setting, then the computational pages are fair game for stealing (paging out) to replenish the free list. With the default setting of 20, this might be your problem.


Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L