Re: vm issues on sap app server

From: Dejan Muhamedagic (dejan@hello-penguin.com)
Date: Thu Feb 20 2003 - 09:05:59 EST


Rik,

On Thu, Feb 20, 2003 at 10:21:50AM -0300, Rik van Riel wrote:
> On Thu, 20 Feb 2003, Dejan Muhamedagic wrote:
>
> > # mem | grep Cache
> > Cached: 4569128 kB
> > SwapCached: 829668 kB
> > ActiveCache: 136728 kB
>
> The "problem" here is that a lot of the memory in Cached: is
> mapped into process address space, so in effect it is process
> memory.
>
> This is especially true for executables, libraries and shared
> memory segments, which you REALLY want to have treated as process
> memory and not as cache...
>
> This makes the Cached statistic a bit confusing for administrators.

Is there a way to split the statistics? It also sounds confusing :)

> > > In that case you're probably familiar with the cache size
> > > tuning, since AIX has the exact same tuning knob as rmap ;)
> >
> > AIX vmtune -P is equivalent to the Linux cache-max, but cache-max
> > is not implemented.
>
> Doesn't it also have something like the borrow percentage, above
> which AIX will only reclaim from the cache, unless the repaging
> rate of the cache is higher than that of process memory ?

No, not that I'm aware of. You can check the man page for vmtune
yourself:

http://publibn.boulder.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds6/vmtune.htm

BTW, there is also quite a bit of interesting documentation about
the AIX VMM.

Cheers!

Dejan
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