HP-UX 11i Release Notes (December 2000)

Process, Threads, Memory, and Kernel Parameters
Large Private Data Space (new)
Chapter 8 157
Large Private Data Space (new)
This change increases the amount of private data space available for a
process. An additional 1 to 2GB of private address space is now
supported for 32-bit programs (if enabled on a per process basis), at the
expense of shared memory address space.
New Options
Two new options have been added to the chatr(1) command that allow
the user to control whether the 3rd quadrant (the 1GB of address space
from 0x80000000-0xBFFFFFFF) and the 4th quadrant (the 1GB of
address space from 0xC0000000-0xFFFFFFFF) of a process are part of the
processes private address space or are shared with other running
processes. Previously, the 3rd and 4th quadrants were dedicated for
shared object usage, e.g. System V shared memory and memory mapped
files using a shared mapping (MAP_SHARED).
The new options are:
• +q3p <enable/disable>
• +q4p <enable/disable>
See the chatr (1) manpage for more details.
In order to use this new feature, the maxdsiz kernel configurable
variable will need to be increased appropriately. Also, the system will
have to enable enough swap space to support processes with large
private address spaces.
Compatibility Issues
Processes that enable a private 3rd quadrant (q3p processes) will
reduce the amount of address space available for shared objects by 1GB.
Also, q3p processes will not be able to share objects that were created
by another non-q3p process, even in the 4th quadrant, unless those
objects were created by the non-q3p process using the IPC_GLOBAL flag
(System V shared memory) or MAP_GLOBAL flag (mmap). If recompiling is
not an option, it will be necessary to make all processes that share
objects with the q3p process into q3p processes (chatr +q3p enable
<a.out> ).