Accessing more than 1.0 GB of data on AIX

 

This section describes necessary settings to get access to more than 1.0 GB on AIX for allocations of data within a V5 process.

Background

This behavior is only applicable to 32-bit Version 5 processes.

By default, Version 5 processes (32-bit) on AIX can allocate up to 1.0 GB. It is possible to override the default allocation capabilities up to 2.0 GB. Such a capability requires additional tunings in order to be effective :

Operating System required customizations

To get access to more than 1.0 GB for allocating data, the X server must be configured to use extended shared memory. To enable this support, do the following :

  1. Modify /usr/lpp/X11/defaults/xserverrc shell script to add :
    EXTSHM=ON
    export EXTSHM

    before execution of the X process in the shell script (for example, just before environment variable EXTENSIONS is set in the shell script).
  2. Reboot workstation or restart the X server to take modification into account.

Version 5 required customizations

Large Memory Model

The capability to allocate more than 1.0 GB on AIX is controlled by an environment variable : V5MEM. This environment variable can take an integer value from 5 to 8 , and controls the number of 256 MB segments that Version 5 can allocate. By default, this environment variable is not set. When set, the environment variable is checked by catstart shell script, which will set the environment accordingly.

Very Large Memory Model

Under AIX 5.2 and AIX 5.3 running the 64-bit kernel, Version 5 will be able to allocate up to 2.25 GB, but the following customization is required:

Additional Operating System considerations