Essay About Memory Windows And Hp-Ux

4quadrant Hp-Ux Memory Issue
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Memory Windows in HP-UX 11.0. White Paper
page 1
Memory Windows
White Paper
1. Objectives
HP-UX release 11.0 is the first to support the new HP V-class machine. Targeted for high end OLTP, decision
support, server consolidation and ERP, the V-class can support up to 16 gigabytes of physical memory.
The current 32-bit virtual address space of HP-UX is limiting applications from taking full advantage of
systems with a large amount of physical memory.
Not all of HPs software providers have ported their applications to 64-bits, nor is it necessary in all cases.
But HP-UX has limitations for shared resources on 32-bit applications. All applications in the system are
limited to a total of 1.75 gigabytes of global space(shared memory), 2.75 gigabytes if compiled, linked as
EXEC_MAGIC and chatrd as SHMEM_MAGIC. In a system with 16 gigabytes of physical memory, only
1.75 can be used for shared resources such as shared memory.
To address this limitation a functional change has been made to the 11.00 release of HP-UX. The patch
allows 32-bit processes to create unique memory windows for shared objects like shared memory. There
are three types of executables in HP-UX. Their layout *WITHOUT* memory windows is the following:
The default HP-UX memory management is based on quadrants where each process has its own space.
The process text (executable code) is mapped to quadrant 1 and its private data is mapped to quadrant 2
in its individual space. Quadrant one and two exists n times (once for each process). All shared objects are
mapped to quadrant 3 and 4 (and quad 2 for SHMEM_MAGIC) of one single space shared by all processes.
This is where the system wide limit of 1.75 Gbs comes from. Each quadrant is 1gigabyte in size.
Program Text
1 Gigabyte
(quadrant 1)
Program Data
1 Gigabyte
(quadrant 2)
Global Space
1 Gigabyte
(quadrant 3)
Global Space
.75 Gigabyte
(quadrant 4)
Program Text & Data
1 Gigabyte
(quadrant 1)
Program Data
1 Gigabyte
(quadrant 2)
Global Space
1 Gigabyte
(quadrant 3)
Global Space
.75 Gigabyte
(quadrant 4)
Program Text & Data
1 Gigabyte
(quadrant 1)
Global Space
1 Gigabyte
(quadrant 2)
Global Space
1 Gigabyte
(quadrant 3)
Global Space
.75 Gigabyte
(quadrant 4)
SHARE_MAGIC
(default)
EXEC_MAGIC SHMEM_MAGIC
Memory Windows in HP-UX 11.0 White Paper
page 2
The 4th quadrant is only .75 gigabytes in size because the last 1/4 of the quadrant is reserved for architected
I/O space.
By default all executables are SHARE_MAGIC, the default mode. EXEC_MAGIC and SHMEM_MAGIC
require special binaries.
If no special options are given to the compiler/linker, the default executable format is SHARE_MAGIC. Text
is shared for all copies running on the system and data is private. EXEC_MAGIC is the output of using the
-N option to the linker. It results in the data starting immediately after the text allowing for a greater sized
data space (approximately 1.9 Gbs). SHMEM_MAGIC combines all the pieces of a process into the first
quadrant (text, data, and stack). SHMEM_MAGIC was done at a time when only 32-bit kernels were supported.
Applications requiring more than 1.75 Gbs of shared space should recompile as 64-bit and then
memory windows is not needed.
Unless otherwise noted, the remainder of this paper assumes the default executable format of
SHARE_MAGIC.
Memory windows allows each process to define a unique global space of up to 1 gigabyte of shared memory.
Shared memory segments placed in the unique space can only be accessed by processes in the
same memory window. But different applications, or distinct instances of a single application, can be
placed in different memory windows and consume more of the available physical memory within the system.
Memory windows extends system wide virtual capacity for 32-bit applications only. By extending the virtual
capacity, more of the underlying physical memory can be used for shared objects. Without memory
windows