eqmemsize(5)eqmemsize(5)NAMEeqmemsize - 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
(see eqmem_limit(5)).
Note that generally speaking, systems where it was useful to set will
not need to set
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 applications 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 poten‐
tially 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 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 tun‐
able.
The equivalent memory allocator was completely rewritten after HP-UX
11i Version 2. The current version of the equivalent memory allocator
decides, at boot, which pages it will consider to be equivalently map‐
pable. It makes the corresponding virtual addresses unavailable for
other purposes, thereby ensuring that if the physical page is avail‐
able, 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 tunable places
a cap on the total amount of memory which will be considered equiva‐
lently mappable.
Such pages are treated almost identically to other pages, but not
quite. The differences only matter on Cache-Coherent Non-Uniform Mem‐
ory Access (ccNUMA) systems, where in some circumstances these differ‐
ences can result in reduced performance. On such systems the tunable
may be used to reduce the total amount of memory that will be desig‐
nated equivalently mappable down to the maximum 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
was developed by HP.
SEE ALSOeqmem_limit(5).
OBSOLETED Tunable Kernel Parameters eqmemsize(5)