eqmem_limit.5 (2010 09)

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eqmem_limit(5)
PA-RISC System Only
eqmem_limit(5)
(Tunable Kernel Parameters)
It is not especially useful to change this tunable on systems which support neither online memory addi-
tion nor cell local memory. It’s also generally not especially useful to change it on small ccNUMA sys-
tems, having only a handful of localities (cells).
The default value is extremely conservative, and should support online addition of more memory than is
actually possible, with lots of equivalently mappable memory left over for the rare applications and
drivers which might need it -- provided that there’s sufficient physical memory that’s actually equivalently
mappable (non-ejectable, not cell local, and having physical addresses in the legal range for kernel
dynamic virtual addresses). However, memory designated as equivalently mappable may be used for
other purposes, and it’s conceivable that usage patterns might result in its unavailability when needed for
OLA. If such a problem is encountered, it may be useful to raise the tunable value above the computed
default value. (This should probably be done only on the advice of HP customer support engineers.)
What Are the Side Effects of Changing the Value?
If the total amount of memory designated as equivalently mappable is too low, allocations will fail. This
can result in the failure of online addition of memory, or of devices whose drivers require equivalent
memory.
If the total amount of memory designated as equivalently mappable is too high somewhat reduced perfor-
mance may be experienced for accesses to shared structures on ccNUMA systems.
Values above 104856 (1024 * 1024 MB, i.e. 1 Terabyte) are unsupported, and should be avoided except on
the advice of a customer support engineer.
What Other Tunable Values Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at
http://www.hp.com/go/hpux-core-docs
.
AUTHOR
eqmem_limit was developed by HP. kctune(1M).
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: September 2010