eqmemsize.5 (2010 09)

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eqmemsize(5)
OBSOLETED eqmemsize(5)
(Tunable Kernel Parameters)
NAME
eqmemsize - determines the minimum size (in pages) of the equivalently mapped reserve pool
(OBSOLETED)
DESCRIPTION
This tunable has been obsoleted and removed.
If it is desired to control the total amount of equivalently mapped memory available to the kernel after
boot, then use the new tunable eqmem_limit
(see eqmem_limit (5)).
Note that generally speaking, systems where it was useful to set
eqmemsize will not need to set
eqmem_limit.
Equivalently mapped memory is memory which is given the same physical and virtual address. On PA-
RISC systems, this is required to support on-line addition of memory, and may be useful for some applica-
tions and some I/O devices.
HP-UX 11i Version 2 maintained a (small) reserve of equivalently mapped pages, which could be used for
no other purpose. It could also potentially equivalently map any page having a physical address below
the maximum kernel virtual address, but only if it happened to find both the virtual and physical
addresses available; this rarely happened, except immediately after boot. The
eqmemsize tunable was
used to size this reserve. It was kept quite small, except on systems known to use such memory, where
the reserve pool size would be increased using the
eqmemsize tunable.
The equivalent memory allocator was completely rewritten after HP-UX 11i Version 2. The current ver-
sion of the equivalent memory allocator decides, at boot, which pages it will consider to be equivalently
mappable. It makes the corresponding virtual addresses unavailable for other purposes, thereby ensur-
ing that if the physical page is available, it will be possible to map it equivalently. This allows such pages
to be used for other purposes, and still be reliably reused for equivalent mappings. Thus no reserve is
required. The
eqmem_limit tunable places a cap on the total amount of memory which will be con-
sidered equivalently mappable.
Such pages are treated almost identically to other pages, but not quite. The differences only matter on
Cache-Coherent Non-Uniform Memory Access (ccNUMA) systems, where in some circumstances these
differences can result in reduced performance. On such systems the
eqmem_limit tunable may be used
to reduce the total amount of memory that will be designated equivalently mappable down to the max-
imum expected to actually be needed. (Normally the kernel makes a very conservative estimate of the
total amount that might be needed.) See eqmem_limit (5) for details.
AUTHOR
eqmemsize was developed by HP.
SEE ALSO
eqmem_limit(5).
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1