HP-UX Virtual Partitions Administrator's Guide (includes A.05.02)

CPU, Memory, and I/O Resources (A.05.xx)
Memory: Concepts and Functionality
Chapter 6
198
NOTE WLM and Dynamically Migrating Memory in vPars
If WLM is managing the target virtual partition, the WLM daemons wlmpard and wlmd should
be stopped prior to execution of the vparmodify command to migrate the memory. For more
information, see the WLM A.03.02 Release Notes at http://www.hp.com/go/wlm.
NOTE Granules and Memory Migration
When memory is deleted from an UP virtual partition, the actual amount deleted may not be
what is specified on the command line. First, memory is always migrated (added or deleted) in
terms of memory granules. The vPars Monitor rounds up to the next granule size. For example,
if a 100 MB memory deletion request is made and the memory granularity is set to 256 MB,
256 MB will be deleted - not 100 MB. If a 257 MB deletion is requested, 512 MB will be deleted.
To minimize any unintended changes, you can perform memory migrations in terms of
multiples of the granule size.
Another reason for a difference between the specified amount on the command line and the
actual amount is memory alignment: whether the target virtual partition has float memory
granules that are aligned on a granular boundary.
In a vPars system, a few memory granules may not conform to the specified granule size. For
example, even if the specified granule size is 256 MB, there may be memory granules that are
less than 256 MB. Within a granule, the firmware may use a portion of the memory granule
even before the vPars Monitor boots, or memory pages in the system may be bad due to double
bit memory errors.
For example, if we have the following configuration:
• The specified ILM granule size is 256 MB.
• vpar1 contains 500 MB of float memory made up of two granules, 256 MB and 244 MB.
If you request a deletion of 244 MB, the vPars Monitor rounds up the request to the specified
granule size of 256 MB and passes the request to the OS kernel. The kernel chooses one of the
float memory granules for deletion. The chosen granule can be either the 244 MB or 256 MB
granule. If the kernel chooses the 256 MB granule, then the amount of memory that is deleted
is different from the request of 244 MB. The contrary is true, where if you request a 256 MB
deletion, the kernel may choose the 244 MB granule Again, the memory deleted (244 MB) is
different from the command line request of 256 MB.
For further information on memory usage, see Appendix D, “Memory Usage with vPars in
nPartitions,” on page 361.
Advanced Topic: Granularity
Granularity refers to the unit size in which memory is assigned to the all virtual partitions in a given vPars
database (vpdb). You should be careful when using the granularity option; using the granularity option
incorrectly can cause all the virtual partitions to not be bootable.
For information, see:
• “Memory: Granularity Concepts” on page 208
• “Memory: Granularity Issues (Integrity and PA-RISC)” on page 209
• “Memory: Setting the Granularity Values (Integrity)” on page 210