numperm help 1

[lpblauen]

I'm trying to get numperm down from 79% all the time. I set min/maxperm to 20 and maxclient to 20. I still have to much memory going to filesystemcache. Any Ideas? here is nmon output.

FileSystemCache x
(numperm) 79.1%x
Process 2.3%x
System 6.1%x
Free 12.5%x
------x
Total 100.0%x
x
User 80.4%x
Pinned 3.5%x
I get the same reading at 20% or 80% min/max perm.

 

[hirschaj]

If you have maxperm set to 20 and numperm is at 79% that means your system is not trying to use enough computation space so the VMM makes the decision to break the soft limit of maxperm for filesystem cache. This is a good thing...It keeps your system running faster. If you really, really want to make maxperm a hard limit then you can turn on strict_maxperm, but I think it will only slow your system down over time in this case. Hope that helps.


Jim Hirschauer

http://www.aixexpert.com

 

[lpblauen]

What we have is raid adapters that have cache already. I want the adapter cache used not the system memory for cache. I hope this makes cents.

 

[hirschaj]

The cache on a raid adapter is usually pretty small compared to the amount of RAM in a system. At any rate, if you want to try setting up a hard maxperm you need to use the strict_maxperm tunable. Good luck, should be interesting to test and see what happens. Memory tunables are a lot of fun to play with as long as you are not messing with production servers.


Jim Hirschauer

http://www.aixexpert.com

 

[RodKnowlton]

ipblauen,

AIX uses the virtual memory paging mechanism for regular file reads, too. Regular file reads are "paged" (moved one 4k page at a time) into system memory.

The cache on your raid adapter is already being used (assuming it's configured properly), but the caching it does is one level of abstraction below what AIX does. The operating system doesn't distinguish between adapter cached or actual disk data, because it doesn't need to. AIX just tells the adapter "Give me X page(s) from location Y on disk device Z", and the adapter fulfills the request, fetching from its cache if available and otherwise from the disk.

Jim's right, if you have maxperm set that low and it's being exceeded by that much it's because the system doesn't need the memory.

There's no need to be concerned that a process won't get more memory if it needs it, either.

If a process should require additional memory, it'll be allocated in a practically instantaneous manner. Permanent (file) pages that are clean (haven't been written to since last written to disk) don't have to be paged out, they can just be freed.

You can set strict_maxperm, but unless your machine is oversized for its purpose or doesn't use disk very often, you'll regret it.


- Rod

IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

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