AIX Version 4.3 Differences Guide

The locking methodology has been changed to lock the object only for critical
parts of the operation. This will allow other operations on the object to complete
when in the past they may have waited or timed out. For example, this change
will allow a showlog operation to be carried out on a machine resource, which a
customer operation is also being carried out. Previously, the machine object
would be locked for the entire duration of the customer operation.
6.12.3 Administration Enhancements
The NIM sections of SMIT and Web-Based System Manager have been updated
to offer function that was previously only available using the NIM command line
interface. This includes support for ATM network types and IEEE 802.3 Ethernet
networks.
6.13 Paging Space Enhancements (4.3.2)
AIX Version 4.3.2 now provides support for up to 32 GBs of memory on RS/6000
64-bit SMP servers. Before AIX 4.3.2, paging space was allocated for the
executing process at the time the memory was requested or accessed. This
required backing paging space allocated for all pages in the real memory, to save
the image of the page. On a large-memory machine where paging was never or
rarely required, these paging space blocks were allocated but never be used. In
this case, resources were wasted.
In AIX 4.3.2, the policy for paging space allocation has been modified to allow a
deferred paging space allocation. The allocation of paging space is delayed until
it is necessary to page out the page, which results in no wasted paging space
allocation. This new paging space allocation method greatly reduces the paging
space requirements for systems with large physical memory.
6.13.1 Late and Early Paging Space Allocation
There are three kinds of paging space allocation policies used with AIX. The
setting of the PSALLOC environment variable determines the paging space
allocation mode.
Early Allocation
If the environment variable PSALLOC is set to early, then the early allocation
policy is used. This will cause a disk block to be allocated whenever a memory
request is made. If there is insufficient paging space available at the time of the
request, the early allocation mechanism fails the memory request. This
guarantees that the paging space will be available if it is needed.
Late Allocation in Pre-AIX 4.3.2
If the environment variable is not set, then the default late allocation policy is
used and a disk block is allocated only when a page in memory is initially
accessed, not when it is allocated.
Late Allocation in AIX 4.3.2
AIX 4.3.2 modifies the late allocation policy so that a disk block is not allocated
until it becomes necessary to page out the page from memory into paging space.
In AIX 4.3.2, late allocation will not allocate any disk blocks if there is enough real
memory and no paging required for a given application set.
System Management and Utilities 137