Configuring and Migrating Memory on vPars

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a system with all base memory might perform better compared with another system
with the same amount of memory but divided between base and floating memory.
Ø Some kernel sub-systems and applications do their allocations based on memory
discovered during boot time. These subsystems or applications might allocate their
cache based on the amount of base memory available to the kernel during boot time
and might not scale that cache when more base memory is later added online. Hence,
the performance of a system that is booted with less memory followed by online add of
memory might not be equal to a system with the same amount of memory but all
available during boot.
• For processor and I/O resources in a given locality, the kernel might optimize the memory
access latency by allocating data structures from base memory within that locality. Hence, it is
better to configure some amount of base memory from a cell if the partition is going to have
processors and I/O from the same cell.
• Initial measurement has shown that the HP-UX kernel takes about 1 second to add or delete 1
GB of memory on an idle or lightly loaded system. In addition to the time taken by the HP-UX
kernel, the vPars commands and monitor might take additional time of up to a second to
process addition or deletion. The times quoted here can increase in future releases. On the
other hand, on a system with heavy memory pressure, the HP-UX kernel might take minutes or
even hours to evacuate memory. Hence, it is advisable not to delete memory on a loaded
system. Such a constraint does not exist while adding more memory. The system administrator
can add memory anticipating memory load or during memory load.
Ø When system takes more time to delete or does not make forward progress on
deletion, it may be helpful to cancel the operation (cancel is discussed in the “Memory
Migration Management” chapter) and split the single large memory delete operation
into two or more small memory delete operations. For example, if the partition contains
a large amount of floating memory, instead of deleting all the floating memory in one
delete operation, it may help to split it into multiple small delete operations each
consisting of 10% to 25% of floating memory.
• The HP-UX kernel requires a certain percentage of total memory to be base memory to assure
expected system performance and ensure that there is adequate memory for critical system
needs. The following table shows the minimum amount of memory that must be configured as
base memory for a given total memory size. Some applications may need more base memory
than what is recommended below.
Physical Memory
(total)
Base Memory
(minimum)
1.5 GB to 3 GB 1.5 GB
3
3 GB to 8 GB ½ of physical memory
8 GB to 16 GB 4 GB
>16 GB ¼ of physical memory
During boot, if enough memory is not configured as base, the kernel might convert some of the
floating memory into base. When that happens, the vPars monitor updates the vPars database
to reflect the increase in base memory and decrease in floating memory for that partition.
3
The HP-UX 11i v3 requires minimum of 1.5GB of base memory.