HP-UX Virtual Partitions Administrator Guide (includes A.05.07) (5900-1229, September 2010)

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 (page 319).
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 ” (page 195)
• “Memory: Granularity Issues (Integrity and PA-RISC)” (page 196)
• “Memory: Setting the Granularity Values (Integrity)” (page 197)
• “Memory: Setting the Granularity Values (PA-RISC)” (page 200)
Memory: Concepts and Functionality 189