eqmemsize man page on HP-UX

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eqmemsize(5)							  eqmemsize(5)

       eqmemsize  - determines the minimum size (in pages) of the equivalently
       mapped reserve pool (OBSOLETED)

       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‐

       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.

       was developed by HP.


OBSOLETED		   Tunable Kernel Parameters		  eqmemsize(5)

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