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26 Logical Partitions on System i5

So rather than a memory granularity of 1MB, the System i5 memory granularity will be

between16 MB and 256 MB. Again, this is determined by the system setting for the memory

region size.

With the June 2004 level of code, you can view the LMB size from the HMC by displaying the

Managed Server properties, selecting the memory tab, and you will see the current LMB

setting. In a future code release, you will be able to change the LMB size through the ASM

interface. There will be an option under Performance settings.

Actual memory used for paging and cache are not affected by or have anything to do with the

memory region size.

1.4.2 Memory and LPAR

The assignment of memory to logical partitions in a System i5 V5R3 environment is handled

differently than it has been in the past. Functionally, one of the main benefits for LPAR is that

a partition can utilize all the memory assigned to it.

1.4.3 Hardware page table

The hardware page table (HPT) on systems prior to System i5 was contained within the

memory assigned to the partition. This was treated as hidden or reserved memory. There is

no longer the concept of reserved memory on System i5 hardware. The HPT now exists in

memory that is controlled by pHyp or hypervisor memory. When a partition profile is defined,

the amount of memory designated in the “max” memory parameter affects the size of that

table. This is based on a specified ratio applied against the “max” parameter.

Even though there is no reserved memory, you should still take care when deciding on

memory size and be reasonable about the maximum memory parameter. Because there is no

reserved or “hidden” memory, a partition gets full use of its assigned memory. The Phyp

memory is a part of the total physical memory on a system and it is not specifically for the

HPT. There are other system factors that also affect the amount of memory in Phyp.

However, we are only looking at LPAR memory requirements in this chapter.

1.4.4 Memory assignment at initial LPAR start

When you create a partition profile, you specify the min/current/max memory numbers. Click

the Recalculate button and it shows you what is the minimum memory requirement for that

partition. The minimum required memory is determined by the current/max numbers and the

operating system type that will be run in that partition. For OS/400 partitions, this is either 128

MB or 256 MB depending on the max value. The more common one seems to be 256 MB.

This is referred to as the Real Memory Offset (RMO).

When you start a partition for the very first time, what it does is to look for 256 MB (that

minimum amount) of contiguous memory to be the RMO. This means that with a 16 MB

memory region size, it will need to find 16 contiguous blocks of memory. This memory is

owned by the partition and is entirely usable.

The rest of the partition’s memory does not have to be contiguous but it is also assigned at

the initial start up. Once the partition is associated with all of its physical memory, it then owns

it. That ownership is persistent even if the partition gets powered down. No other partition

may use that memory unless the profile information is overtly changed. When you restart a

partition, it uses the same RMO and memory each time.

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YOGGIE YOGGIE MANAGEMENT SERVER Technical Information Page 44