eqmemsize(5) File Formats Manual eqmemsize(5)
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
(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
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 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
tunable.
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 mappable. It makes the corresponding virtual addresses unavailable for
other purposes, thereby ensuring 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 tunable
places a cap on the total amount of memory which will be considered 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 tunable may
be used to reduce the total amount of memory that will be designated 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 ALSO
eqmem_limit(5).
OBSOLETED
Tunable Kernel Parameters eqmemsize(5)
