Newsgroups: comp.unix.aix,comp.parallel.pvm
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From: accapadi@austin.ibm.com (Matt Accapadi)
Subject: Re: Q:vmstat, PVM
Sender: news@austin.ibm.com (News id)
Message-ID: <CpAqFw.15t1@austin.ibm.com>
Date: Wed, 4 May 1994 21:02:19 GMT
Reply-To: accapadi@austin.ibm.com
References: <2q4s20$5b4@nuscc.nus.sg>
Organization: IBM, Austin, Tx.
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Xref: ukc comp.unix.aix:38233 comp.parallel.pvm:1709

In article <2q4s20$5b4@nuscc.nus.sg>, Heng Kek <nsrcchk@leonis.nus.sg> wrote:
>From the man pages for the 'vmstat' cmd, the underlined value above
>refers to the 'size of the free list'.  I assume that this means
>'available free memory'(?).  I find that this value dwindles from a
>value of, say 22000 (immediately after a reboot) to a value of 5000
>after running some cpu intensive jobs.  However, after the jobs end,
>the value of the 'free list' doesn't seem to be restored to the
>original 22000.  Why?

Since AIX memory maps files (for performance reasons), your available RAM
is used to cache files.  If your programs access a lot of large files, then
RAM gets used for caching it, but when your programs end, the files stay
in the cache.  This is so that if the file is accessed again, it will still
be there in memory (this is why the free list doesn't get restored).

If memory is needed, then these file pages are paged out.
If you acccess very large files (a good chunk of your RAM anyway), then
you may not want all of your RAM to be used for memory mapping. If not, then
use /usr/lpp/bos/samples/vmtune to decrease the value of maxperm (used to
limit file mapping). By default, AIX uses close to 80% of RAM for memory
mapping.  Make sure you get a more recent version of vmtune rather than
the original one (if you do a what on it, the version should be greater than
1.1).  That's because of a synchronization bug that could manifest itself
if you run vmtune while the VMM is modifying the freelist.

>Also, if the value of the 'free list' is small (say 5000), the
>execution of some PVM jobs seem to be affected in a rather 'bad'
>way.  i.e. they get killed at random!  I'm not sure if this happens
>for the 'ordinary' (non-PVM) jobs.

A freelist of 5000 is not small at all - that's almost 20M!).  Of course,
PVM may get kinda large I suppose.  If your jobs are getting killed, run
"errpt" to see there were any paging space kills.

>If so, what has been done to rectify such a situation?

If you still have problems, open a performance pmr (tell them to queue it
to l3perf).

>Is this a bug with Aix?
No.


_____________________________________________________________________________

Mathew Accapadi                          Internet: accapadi@austin.ibm.com
IBM Risc System/6000 Division            RS/6000: POWER PACKED, POWER BACKED!
AIX System Performance                   VNET:  ACCAPADI at AUSTIN
11400 Burnet Rd. Bld. 906/9632           yaknet: 512-838-3193  Tie 678-3193
Austin, TX 78758-3493                    fax: 512-838-1801

DISCLAIMER:  The above does not represent the opinions of my employer.
_____________________________________________________________________________

