topic Re: process memory usage in 10.x machine in Operating System - HP-UX

process memory usage in 10.x machine

dheepak — Wed, 13 Mar 2002 15:47:21 GMT

I understand that when i use "delete" operator call or free() call in c++, i'm releasing memory from the process to the operating system(HP 10.20).
But why does Glance doesnt show the decrease in process memory usage .
even "top" command doesnt reflect the change in the mem. usage of the process?

Re: process memory usage in 10.x machine

harry d brown jr — Wed, 13 Mar 2002 15:56:29 GMT

Because it really doesn't. Part of the schedulers task is to help the system determine what the high and low memory requirements are per process. That way, when/if the process starts to demand more memory, it will already have it reserved. But if the system needs to "reclaim" it, it will.

http://docs.hp.com/hpux/onlinedocs/os/11i/mem_mgt.html

live free or die
harry

Re: process memory usage in 10.x machine

A. Clay Stephenson — Wed, 13 Mar 2002 15:58:07 GMT

Hi:

I can't believe I just answered the same question.

When you free process memory using free(), the memory is not returned to the OS but rather goes back on the process's heap forereuse by the same process. You can use the sbrk() system call with a negative vaue to decrease allocated process space but this is not for the faint of heart. If you use sbrk(), you must not use any of the higher-level memory allocation/free functions or absolute chaos including crashes is almost guaranteed.

Regards, Clay