Tuesday, February 26, 2013

Active Memory Expansion

AME ( Active Memory Expansion):

AME provides the capability to expand the effective memory capacity of a system beyond its physical memory capacity.

AME relies on compression of in-memory data to increase the amount of data can be placed into memory and thus expand the effective memory capacity of a P7 system.

The in-memory data compression is managed by OS and this compression is transparent to application and users.

When AME is enabled for a LPAR, the Operating system will compress a portion of the LPAR’s memory  and leave the remaining portion of memory uncompressed. This results in memory effectively being broken up into 2 pools: Compressed poll and uncompressed pool.

When an application needs data that is compressed, the OS will automatically decompress the data and move it from the compressed pool to uncompressed pool. When the uncompressed pool is full the OS will compress data and move it from the uncompressed pool to compressed pool.

When configuring AME, the memory expansion factor to be set for the LPAR.

LPAR Expanded Memory Size=Real Memory Size of LPAR * Memory Expansion Factor.

AME Supports: - P7 systems, HMC V7R7.1.0.0, eFW: 7.1, AIX: 6.1 TL4 SP2.

AME will not compress File Pages and Pinned virtual Memory Pages.

AME Planning tool (AMEPAT) will monitor existing AIX work load and provide an indication of whether the work load is a good candidate for AME based.

AME requires CPU resource for Memory compression and decompression activity. The amount of CPU required for compression and decompression will vary based on work load.

AME Planning Tool: This tool will monitor a workload’s memory usage and data compressibility over a user-configurable period of time. The tool will then generate a report with a list of possible AME configurations for this workload. This tool is available as part of AIX 6.1 TL4 SP2.
Ex: - amepat 120

Output columns:- System Configuration, System Resource Statistics, AME Modeled Statistics (Expansion Factor, Modeled True memory size, Modeled Memory Gain, CPU Usage Estimate),  AME Recommendation.

AME Configuration:- In LPAR profile à Memory Tab à enable “Active Memory Expansion factor” and mention the Factor value recommended by AMEPAT.

Memory Deficit:- If a LPAR is configured with a memory size of 20 GB and a mmemory expansion factor of 1.5 this results in a total target expanded memory size of 30 GB. However workload compresses in the facror of 1.4. So the expanded memory size that can be achieved is 27.2 GB. There is a short fall of 2.8GB. 2.8 short fall referred as a memory deficit.

Memory expansion factor can be changed dynamically.

Monitoring of AME can be done through AMEPAT. Report attributes à System Configuration (Partition details), System Resource statistics ( CPU Util, Virtual Memory Size, True memory in use, Pinned Memory, File Cache Size, Available Memory), AME Statistics ( AME CPU Usage, Compressed Memory, Compression Ratio).

Vmstat –c à provides compression & decompression statistics.
Lparstat –c à Provides an indication of the CPU Utilization for AME compression & decompression activity
Svmon à view of memory usage broken down into compressed & uncompressed memory.
Topas à will show memory compression statistics

AME & AMS can be used together. If the LPAR enabled with AMS the actual memory can change dynamically. But this will not effect on the LPAR’s expanded memory size.

Page Loaning:- Page Loaning is a feature that enables the hypervisor and OS to collaborate on memory management in the AMS environment. When the hypervisor needs to take physical memory back to the hypervisor, there is a vmo tunable, ams_loan_policy, that controls the aggressiveness of the page loaning.

Normally AIX will satisfy page loaning requests by paging out pages from memory to disk. In the case of a LPAR where both AMS & AME are enabled, AIX will rely on memory compression to satisfy page loaning request.

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