topic the max memory limit for 32-bit apps in Operating System - HP-UX

the max memory limit for 32-bit apps

Arnold_14 — Thu, 27 May 2004 11:15:19 GMT

What is the max memory limit for 32-bit apps? People say it's 2G, but some say it's 3.75G. I have HP-UX 11.11, 64 bit OS.

We have an application that keeps giving us a core dump when the memory usage hits 1946 Mb. And we can repeat this error many many times.

And I believe I can change the maxdsiz kernel parameter to change this setting, correct?

Thanks
Arnold

Re: the max memory limit for 32-bit apps

SIJU JOSE — Thu, 27 May 2004 11:19:51 GMT

Hi

It is 3.75 GB only.It doesnt matter which is your OS.

Siju Jose

Re: the max memory limit for 32-bit apps

Patrick Wallek — Thu, 27 May 2004 11:35:10 GMT

It depends. If I recall correctly, a basic compile of a program will only allow you to use about 2GB. There are certain options you can compile with, I can't recall them right now, that will allow you to use memory from all 4 quadrants in 32-bit programs. That would give you about 3.75GB.

However, you must remember that this amount is SHARE AMONG ALL 32-bit programs. So if you have 1 program that is using 1.5GB, then that cuts down on the amount that other 32-bit programs can use.

If it all possible you should recompile this app as a 64-bit app. That all memory issues are effectively nullified.

Re: the max memory limit for 32-bit apps

Don Morris_1 — Thu, 27 May 2004 11:56:17 GMT

Depends on the flavor/chatr settings. The absolute limit for data is 3.8Gb. To get a chance at that you'd need to be running as EXEC_MAGIC (so text and data are shared) and the set Q3 and Q4 private using chatr.

The default (SHARE_MAGIC) is 1Gb (shared with the stack), EXEC_MAGIC defaults you to 2Gb (text/data/stack share), SHMEM_MAGIC is 1Gb with 3Gb for shared objects.

Re: the max memory limit for 32-bit apps

Ted Buis — Fri, 28 May 2004 09:27:52 GMT

Arnold,

A good white paper to read is on using Memory Windows for 11.0. It applies also to 11i. HP-UX (32-bit) divides the 4GB address space into four quadrants, which can be used in different ways. This has some nice features and some drawbacks, but there are options combine some quadrants to get around the issues. Memory windows helps further so that applications sharing data may be able to get around the 1.75GB limit. Find it at:
http://www.docs.hp.com/hpux/onlinedocs/os/memwn1_4.pdf