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AME on AIX

Posted on 2014-03-18
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Advanced Memory expansion factor on my profile is set to "1", So technically no use, So what is the difference between turning it totally off Vs selecting AME with an expansion factor "1", What are performance implications. Please let me know..
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Question by:aanya247
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woolmilkporc earned 2000 total points
ID: 39937381
The AME factor is an indication of the expected target amount of increased memory.
If your LPAR has let's say 8 GB of memory then, with an AME factor of 2, the OS will report 16 GB of available memory nd the operating system will compress enough in-memory data to fit 16 GB of data into 8 GB of memory.

If you choose an AME factor which is too high there will be a memory deficit and the OS might have to page out virtual memory to page space. "amepat" will show if there is such a deficit.

An AME factor of 1 means that the operating system will not compress any memory.
It's the same as turning AME off, there's no difference.
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by:aanya247
ID: 39937990
So there is no over head on the CPU if I set it to "1" ...??
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by:woolmilkporc
woolmilkporc earned 2000 total points
ID: 39938026
An AME factor of 1 effectively disables it. The remaining CPU overhead, if any, will be very, very low.

You can check the "Active Memory Expansion Statistics" section of "amepat -N" for "AME processor Usage". This will show the CPU overhead.

A maybe more important drawback of keeping AME enabled (even with a factor of 1) is that AIX will solely use 4K pages in that situation. So you don't have multiple page size support, even if AIX is configured for it.
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by:aanya247
ID: 39938114
Ohhh I didnot know that, So first thing how do I check the page size as I know that we have large pages enabled on the server and also on the network.
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by:woolmilkporc
ID: 39938135
vmo  -a | grep lgpg

"lgpg_regions" specifies the number of large pages to reserve, and "lgpg_size" specifies the size in bytes of the hardware-supported large pages.

"vmstat -l" will show the number of large pages in use under "large-page". "alp" is "active large pages" and "flp" is "free large pages".

The network does not come into play here.
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