Configuring and Migrating Memory on vPars

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as well. Assigning processors from one cell and cell local memory from another cell might lead
to less optimal performance due to increased distance between processor and memory locality.
The HP-UX kernel optimizes and performs better when it has processors, memory, and if
possible I/O from the same locality. For more information on processor configuration in a vPars
environment refer to the CPU Configuration Guidelines for vPars white paper [3].
Base and Floating Memory
Starting with the A.05.xx release, online migration of memory is supported on vPars. This means
memory can be added to and deleted from a live vPars partition without requiring reboot. There are
two constraints. First, the HP-UX must be memory migration capable to make use of this feature.
Memory migration capability is present in releases starting with HP-UX 11i v3. Second, on HP
Integrity servers, firmware must also be memory migration capable. Please refer to the HP-UX Virtual
Partitions Ordering and Configuration Guide [4] for the firmware version required for memory
migration.
When memory is added, the HP-UX kernel discovers the new memory, updates its data structures to
include the new memory pages, and allows the applications to make use of the new memory that
became available. When memory is to be deleted, the HP-UX kernel selects the memory pages to
evacuate, moves the contents in that memory to some other free pages or to disk, and then removes
these memory pages from its data structures. After the kernel completes the memory delete operation,
the memory is marked as free and can be assigned to other partitions. Executing the vparstatus
command with the –A option after the completion of the delete operation displays the memory
available for assignment.
During deletion, there are certain memory contents that cannot be evacuated to another free page.
Examples of such contents include kernel code and certain kernel data structures. While allocating
memory during boot or during run-time, the HP-UX kernel needs to know in advance what memory to
use for such contents that cannot be evacuated. To aid the HP-UX kernel in this differentiation, the
vPars software subdivides ILM and CLM into two types: base memory and floating memory.
The system administrator while picking memory for the partition now has four choices: (i) the amount
of ILM that will be base memory, (ii) the amount of ILM that will be floating memory, (iii) the amount of
memory from each cell that will be base memory and (iv) the amount of memory from each cell that
will be floating memory. The ILM and CLM options in the vPars commands have a new attribute that
allows the system administrator to specify whether the memory being added or removed is base or
floating. The amount of memory that is specified as base and floating is stored in the vPars database.
Hence, the amount of memory the partition gets as base and floating persists across partition and
monitor reboots.
During boot or when the memory is added online, the monitor notifies the kernel which memory
pages are base and floating. The kernel uses base memory pages for contents that it cannot
evacuate. On the other hand, for contents that it can evacuate, the kernel will use either floating or
base memory. Hence, memory that is marked as base cannot be deleted when the partition is live. It
can only be deleted when the partition is down. Memory that is marked as floating can be deleted
when the partition is live or when the partition is down.
There is one key differentiation in management of ILM and CLM versus base and floating memory in
the system. If the system administrator has to change the amount of ILM and CLM in the system, it will
require a reboot of the system and the monitor
2
. For example, if the system contains 4 GB of ILM
which is divided among partitions and the system administrator wants to increase the ILM to 6 GB
and reduce the amount of CLM in the system by 2 GB, it will require a system and monitor reboot. On
2
Reboot is necessary because firmware must re-interleave the memory and can do so only with a hard partition reset.