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 :
- From an operating system standpoint
- From a Version 5 standpoint
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 :
- 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).
- 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.
- When V5MEM is not set, Version 5 will be able
to allocate up to 1.0 GB (operating system customizations are not required)
- When V5MEM is set, operating system
customizations are required; V5MEM=5 will give
access to 1.25 GB; V5MEM=8 will give access to
2.0 GB of address space for data allocated during the Version 5 session. In
all cases, it is recommended to have the paging space sized 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:
- required patch : IY53656
- before launching CNEXT :
catstart -run /bin/ksh
export LDR_CNTRL=PREREAD_SHLIB@MAXDATA=0xD0000000@DSA
export MW_GMA_VADDR to 0xD8000000
export DISPLAY=<hostname>:0
export EXTSHM=ON
start CNEXT
Additional Operating System considerations
- One cannot execute a Version 5 session with V5MEM
set simultaneously with another Version 5 session for which
V5MEM is not set. When several session need to
run simultaneously on the same workstation, they should share the same
V5MEM setting, or be executed with
V5MEM unset.
- This behavior is only applicable to 32-bit Version 5 processes, those V5
customizations should be removed for a 64-bit Version 5 process.