AIX Version 4.3 Differences Guide

The default late allocation algorithm for paging space allocation assists in the
efficient use of disk resources and supports applications of customers who wish
to take advantage of a sparse allocation algorithm for resource management.
Some programs allocate large amounts of virtual memory and then use only a
fraction of the memory. Examples of such programs are technical applications
that use sparse vectors or matrices as data structures. The late allocation
algorithm is also more efficient for a real-time, demand-paged kernel, such as the
one in the operating system.
6.13.2 Commands Affected by Late Paging
The following commands are affected by the change in paging policy.
6.13.2.1 vmstat Command Updates
The avm column reported by vmstat command means active virtual pages. In
previous AIX versions, the description of avm states "virtual pages are
considered active if they are allocated". This is not true for every release of AIX
and is changed to "virtual pages are considered active if they have been
accessed".
6.13.2.2 lsps Command Updates
If you set the environment variable PSALLOC=early, the -s flag displays a value
different from the value returned when using the -a flag for all the paging spaces.
In this case, the value of -s flag displays the percentage of paging space
allocated (reserved), whether the paging space has been assigned (used) or not.
The -a flag specifies the percentage of paging space used. Therefore, the
percentage reported by the -s flag is usually larger than that reported by the -a
flag.
The following is an example. First, set the paging space allocation to early:
#export PSALLOC=early
After the system is running for some time, the paging space looks like:
#lsps -a
Page Space Physical Volume Volume Group Size %Used Active Auto Type
hd6 hdisk0 rootvg 256MB 8 yes yes lv
#lsps -s
Total Paging Space Percent Used
256MB 9%
The paging space used reported by using -s (9%) is larger than using -a (8%).
Set the paging space allocation to late:
#export PSALLOC=
The lsps command displays the same percentage value with -a and -s flag (8%).
# lsps -a
Page Space Physical Volume Volume Group Size %Used Active Auto Type
hd6 hdisk0 rootvg 256MB 8 yes yes lv
# lsps -s
Total Paging Space Percent Used
256MB 8%
System Management and Utilities 139