HP-UX 11i June 2003 Release Notes

Process, Threads, Memory, and Kernel Parameters
Memory Windows
Chapter 10
212
Memory Windows
Running without memory windows, HP-UX has limitations for shared resources on
32-bit applications. All applications in the system are limited to a total of 1.75GB of
shared memory (2.75GB if compiled as SHMEM_MAGIC). In a system with 16GB of physical
memory, only 1.75 can be used for shared resources.
To address this limitation, a functional change has been made to allow 32-bit processes
to create unique memory windows for shared objects like shared memory.
The memory window for default executables is 1GB.
This allows cooperating applications to create 1GB of shared resources without
exhausting the system-wide resource. Part of the virtual address space remains globally
visible to all processes, so that shared libraries are accessible no matter what memory
window they are in.
Summary of Changes
The following customer-visible changes have been made for memory windows:
• A new kernel tunable, max_mem_window, allows you to configure the number of
memory windows a system can have.
• A new set of commands and files (setmemwindow, getmemwindow,
/etc/services.window) enables you to start applications in different memory
windows.
• Three manpages for the new functionality have been created: getmemwindow (1M),
setmemwindow (1M), and services.window (4).
See the Memory Windows in HP-UX 11.0 White Paper on http://docs.hp.com for
details.
Compatibility Issues
Incorrect use of memory windows can lead to application failure. Although memory
windows can be applied to any application, that does not mean the application is able to
run in memory windows. Some interfaces may break when used under memory windows.
(Since only the application owner or software provider can certify how and if an
application can run under memory windows, HP does not consider this failure a
compatibility failure.)
CAUTION Errors due to incorrect usage may be subtle and normally not associated with memory
windows.
In many cases software providers may have already certified their applications with
memory windows. Contact HP to see if this is the case.
Configuration
By default, HP-UX ships with memory windows disabled.