Gauging the Benefits of AME

Edit: In the first paragraph I was able to download the audio presentation and the movie. I wonder how long that will last. The whitepaper links no longer work. The report is still available to download but I imagine the link will go away in the future. Instead of downloading the report, I included it at the end of this post.

Originally posted May 17, 2010 on AIXchange

The AIX Virtual User Group-Central Region USA put on another great webinar in April; this one covers Active Memory Expansion (AME). IBMer Nigel Griffiths provides a wealth of information that can help you get up to speed on the topic. The user group Web site has a complete webinar archive, including  Nigel’s audio presentation and related materials. You can also watch this movie at IBM developerWorks.

On the subject of AME, check out a couple of whitepapers. The first is the AME Overview and Usage guide. From IBM:

“IBM’s POWER7 systems with AIX feature Active Memory Expansion, a new technology for expanding a system’s effective memory capacity. Active Memory Expansion employs memory compression technology to transparently compress in-memory data, allowing more data to be placed into memory and thus expanding the memory capacity of POWER7 systems. Utilizing Active Memory Expansion can improve system utilization and increase a system’s throughput. This paper provides an overview of POWER7’s Active Memory Expansion technology, as well as guidance on how to deploy and monitor workloads with Active Memory Expansion.

“Active Memory Expansion increases a system’s effective memory capacity. The additional memory capacity made available by Active Memory Expansion enables a system to do more work, leading to an increase in the system’s throughput and utilization. Thus, the value of Active Memory Expansion is that it enables a system to do more work by increasing a system’s effective memory capacity.”

This whitepaper goes into different scenarios that you might consider when thinking about deploying AME, including expanding consolidation by fitting more LPARs onto your frame and increasing LPAR throughput by increasing the effective memory size of a single LPAR.

The second whitepaper is entitled “AME Performance.” Again, from IBM:

“This document introduces the basic concepts of Active Memory Expansion, showing the principles of operation and performance characteristics of this new component of AIX. Active Memory Expansion is available on POWER7 platforms starting with AIX 6.1 TL04 SP2. All computers have a limited amount of Random Access Memory (RAM) in which to run programs. Therefore, one of the perennial design issues for all computer systems is how to make the best use of the entire RAM which is physically available in the system, in order to execute as many programs concurrently as possible, in the limited space available. Active Memory Expansion, a POWER7 feature, supplies a new technique for making better use of RAM: Portions of programs which are infrequently used are compressed into a smaller space in RAM. This, in turn, expands the amount of RAM available for the same or other programs. Among the benefits of Active Memory Expansion, this paper shows the following scenarios and their performance results:

“1. Reducing the physical memory requirement of an LPAR resulting in 111 percent memory expansion.
2. Increasing the effective memory capacity and throughput of a memory constrained LPAR resulting in a 65 percent increase in application throughput.
3. Enabling consolidation of more LPARs onto a system resulting in a 60 percent increase in overall system throughput.”

If you have AIX 6.1 TL04 SP2 on POWER4, POWER5, POWER6 or POWER7 hardware, running the amepat command can give you an idea of AME’s potential benefits. The idea is to run the command while your system is busy and memory is in use.

When I ran amepat on a fairly idle test machine, I received this report: (Download AIXchange 5.18.10 report)

Take the time to investigate whether your computing environment can benefit from AME.

—— Below this was originally a download file ——

#amepat 1

Command Invoked                : amepat 1

Date/Time of invocation        : Thu Apr 29 11:21:23 CDT 2010

Total Monitored time           : 1 mins 6 secs

Total Samples Collected        : 1

System Configuration:

———————

Partition Name                 : testlpar

Processor Implementation Mode  : POWER7

Number Of Logical CPUs         : 8

Processor Entitled Capacity    : 0.20

Processor Max. Capacity        : 2.00

True Memory                    : 3.00 GB

SMT Threads                    : 4

Shared Processor Mode          : Enabled-Uncapped

Active Memory Sharing          : Disabled

Active Memory Expansion        : Disabled

System Resource Statistics:               Current

—————————          —————-

CPU Util (Phys. Processors)               0.03 [  2%]

Virtual Memory Size (MB)                  1075 [ 35%]

True Memory In-Use (MB)                   3058 [100%]

Pinned Memory (MB)                         567 [ 18%]

File Cache Size (MB)                      1963 [ 64%]

Available Memory (MB)                     1883 [ 61%]

Active Memory Expansion Modeled Statistics:

——————————————-

Modeled Expanded Memory Size   :   3.00 GB

Average Compression Ratio      :   2.63

Expansion    Modeled True      Modeled              CPU Usage

Factor       Memory Size       Memory Gain          Estimate

———    ————-     ——————   ———–

     1.00          3.00 GB         0.00 KB [  0%]   0.00 [  0%]

     1.09          2.75 GB       256.00 MB [  9%]   0.00 [  0%]

     1.20          2.50 GB       512.00 MB [ 20%]   0.00 [  0%]

     1.33          2.25 GB       768.00 MB [ 33%]   0.00 [  0%]

     1.50          2.00 GB         1.00 GB [ 50%]   0.00 [  0%]

     1.71          1.75 GB         1.25 GB [ 71%]   0.00 [  0%]

Active Memory Expansion Recommendation:

—————————————

The recommended AME configuration for this workload is to configure the LPAR with a memory size of 1.75 GB and to configure a memory expansion factor of 1.71.  This will result in a memory gain of 71%. With this configuration, the estimated CPU usage due to AME is approximately 0.00 physical processors, and the estimated overall peak CPU resource required for the LPAR is 0.03 physical processors.

NOTE: amepat’s recommendations are based on the workload’s utilization level during the monitored period. If there is a change in the workload’s utilization level or a change in workload itself, amepat should be run again. The modeled Active Memory Expansion CPU usage reported by amepat is just an estimate.  The actual CPU usage used for Active Memory Expansion may be lower or higher depending on the workload.