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Modifying the no. of mempools and its effect on Aix - No AMS in effect

Posted on 2011-09-15
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Last Modified: 2013-11-17
Please note:  No AMS is active in our environment.

On several  Aix servers, 'memory pools'(vmstat -v) variable is different, irrespective of whether they have same physical memory or not.  All of running  Aix 6.1.TL06,  and 'mempools' is dynamic and cannot be modified using 'vmo'.   Please clarify my questions as below:

1.     Is it possible to keep the 'memory pools' to one?
2.     Keeping "memory pools" to one is better or higher number is better?
3.     How Aix decides, how many memory pools to create?

Thanks and appreciate every response.
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Question by:balasundaram_s
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woolmilkporc earned 500 total points
ID: 36543936
Hi,

"mempools" is deprecated and is no longer tunable.

The number of memory pools can be influenced by tuning "cpu_scale_memp",
which is the number of CPUs per memory pool. By default this value is "8",
which means that from the 9th CPU on you will have at least 2 mempools,
from the 17th on there will be 3 pools etc.
"At least" because there is a dependency on the amount of real memory. The more real memory, the higher the number of mempools, but I admit that I'm not aware what the exact algorithm is.

The allowable range is 1-128 (AIX 5) resp. 4-64 (AIX 6).

Tuning cpu_scale_memp requires the "-r" (reboot) flag and also requires running bosboot before rebooting (vmo will offer running bosboot on your behalf).

Lowering the number of mempools (by raising cpu_scale_memp) can reduce contention between pools.

The default of 8 is recommended, however, and should only be changed if there are very good reasons to do so. At the moment I'm not aware of any.

wmp



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by:balasundaram_s
ID: 36560618
Though 'cpu_scale_memp' is 8 across all the servers, mempools is different irrespective of the memory. Some of the servers are given below:

6GB of memory has 6 mempools
9GB of memory has 1 mempool
6GB of memory has 2 mempools
20GB of memory has 4 mempools.

In the past, 'mempools' served as one of the base value for calculating other parameters.
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by:woolmilkporc
ID: 36561515
Do all your servers have the same number of processors (virtual CPUs in case of LPAR)?
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by:balasundaram_s
ID: 36561658
All are LPARs and details given below:

6GB of memory has 6 mempools  -  4 proc, 512M paging
9GB of memory has 1 mempool    -  2 proc, 8GB paging
6GB of memory has 2 mempools  -  2 proc, 2GB paging
20GB of memory has 4 mempools - 6 proc, 12GB paging

Thanks.
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by:woolmilkporc
ID: 36561712
Except for the last one these values are not really explainable, at least not for me.

Or is it a Power7 machine with SMT factor 4 in effect on some or all of the LPARs?
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by:balasundaram_s
ID: 36563108
smt=2
6GB of memory has 6 mempools  -  4 proc, 512M paging (Power5)
9GB of memory has 1 mempool    -  2 proc, 8GB paging (Power6)
6GB of memory has 2 mempools  -  2 proc, 2GB paging (Power5)
20GB of memory has 4 mempools - 6 proc, 12GB paging (Power6)

Since its all dynamic, I think, I should not look for any logic.  

Thanks for your time, appreciate it.
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