05-06-2011
Quote:
Originally Posted by
alister
Incorrect. The "dynamic portion of the data segment" is delimited by the break. The break is manipulated with the brk() and sbrk() system calls.
Yes you are right the heap is capped by the break pointer...and mmap allocates memory in the hole between break and the upper bound of the stack segment.
Quote:
Originally Posted by
alister
As its name implies, the segment is contiguous. mmap(), however, is allowed to map/allocate memory at random locations in non-contiguous segments beyond the break. Such behavior has nothing to do with the heap.
All segments are contiguous virtually speaking but none are contiguous physically.
Quote:
Originally Posted by
alister
Perhaps your mmap implementation does not do so, but there's nothing to forbid it.
mmap is only used in openbsd for dynamic storage allocation and since my system isnt openbsd it still uses malloc.
Quote:
Originally Posted by
alister
Alternatively, you have a very loose definition of "data segment".
That might be true as anything between the text and stack segment i'm calling collectively the data segment
10 More Discussions You Might Find Interesting
1. Filesystems, Disks and Memory
I'm a new guy to this field and I'm learning a lot about UNIX! Can any explan to me what exactly does 'heap size' mean and how can i increase the size for AIX 4.3.3? (2 Replies)
Discussion started by: i2admin
2 Replies
2. Filesystems, Disks and Memory
Hi all,
Thanks 'thehoghunter' and 'hugo' for the comments!
I've to increase the size of the heap size for AIX 4.3.3. Now what's the command that I've and also is it something similar to growing the file system in Solaris (growfs) (1 Reply)
Discussion started by: i2admin
1 Replies
3. UNIX for Advanced & Expert Users
I'm running websphere 4.5 on AIX 5 with java 1.3 and would like to find out the following: How much memory is allocated to each JVM, and how much of the allocated heap size is actually being used by a specific JVM? (0 Replies)
Discussion started by: rein
0 Replies
4. Solaris
hi all,
in my server there are some specific application files which are spread through out the server... these are spread in folders..sub-folders..chid folders...
please help me, how can i find the total size of these specific files in the server... (3 Replies)
Discussion started by: abhinov
3 Replies
5. Shell Programming and Scripting
Hello,
has anyone written something that will monitor/gather weblogic heap info ? I need to gather size, high/low stats to a file that I can upload to a speadsheet
thanks for your help! (2 Replies)
Discussion started by: galenw
2 Replies
6. Shell Programming and Scripting
Hi Friends,
i need a unix command to check the heap space availability on unix system as I am getting following error:
Error occurred during initialization of VM
Could not reserve enough space for object heap
Error occurred during initialization of VM
Could not reserve enough space for... (2 Replies)
Discussion started by: Anji
2 Replies
7. HP-UX
Hi,
Am new to HP UX , is there a way to find out the size of memory allocated to a pointer on hp ux?
For example we can use the _msize() on windows to find the size of memory allocated to a pointer .
#include <stdio.h>
#include <malloc.h>
void main()
{
void *buffer; ... (0 Replies)
Discussion started by: Wkdunreal
0 Replies
8. UNIX for Dummies Questions & Answers
Hi
I have one Java application installed in my Solaris system. Is there a way to find out the heap memory allocated size/used size/free size for the particular Java process?
If anyone knows the command, please let me know. Even I appreciate if I have any scripts to find out the same.
... (0 Replies)
Discussion started by: nthiruvenkatam
0 Replies
9. UNIX for Dummies Questions & Answers
Hello,
I need to find the total allocated disk space for the home directory.
How can i find that in unix?(in GB).
Thanks. (4 Replies)
Discussion started by: kailash19
4 Replies
10. Solaris
Hi,
the /tmp size is less whereas the size allocated to swap is quite big. how to increase the size of /tmp -
#: swap -l
swapfile dev swaplo blocks free
/dev/md/dsk/d20 85,20 8 273096 273096
#: swap -s
total: 46875128k bytes allocated + 2347188k reserved =... (2 Replies)
Discussion started by: psb74
2 Replies
BRK(2) BSD System Calls Manual BRK(2)
NAME
brk, sbrk -- change data segment size
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
int
brk(const void *addr);
void *
sbrk(intptr_t incr);
DESCRIPTION
The brk() and sbrk() functions are legacy interfaces from before the advent of modern virtual memory management.
The brk() and sbrk() functions are used to change the amount of memory allocated in a process's data segment. They do this by moving the
location of the ``break''. The break is the first address after the end of the process's uninitialized data segment (also known as the
``BSS'').
The brk() function sets the break to addr.
The sbrk() function raises the break by incr bytes, thus allocating at least incr bytes of new memory in the data segment. If incr is nega-
tive, the break is lowered by incr bytes.
NOTES
While the actual process data segment size maintained by the kernel will only grow or shrink in page sizes, these functions allow setting the
break to unaligned values (i.e., it may point to any address inside the last page of the data segment).
The current value of the program break may be determined by calling sbrk(0). See also end(3).
The getrlimit(2) system call may be used to determine the maximum permissible size of the data segment. It will not be possible to set the
break beyond ``etext + rlim.rlim_max'' where the rlim.rlim_max value is returned from a call to getrlimit(RLIMIT_DATA, &rlim). (See end(3)
for the definition of etext).
RETURN VALUES
The brk() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the
error.
The sbrk() function returns the prior break value if successful; otherwise the value (void *)-1 is returned and the global variable errno is
set to indicate the error.
ERRORS
The brk() and sbrk() functions will fail if:
[EINVAL] The requested break value was beyond the beginning of the data segment.
[ENOMEM] The data segment size limit, as set by setrlimit(2), was exceeded.
[ENOMEM] Insufficient space existed in the swap area to support the expansion of the data segment.
SEE ALSO
execve(2), getrlimit(2), mmap(2), end(3), free(3), malloc(3)
HISTORY
The brk() function appeared in Version 7 AT&T UNIX.
BUGS
Mixing brk() or sbrk() with malloc(3), free(3), or similar functions will result in non-portable program behavior.
Setting the break may fail due to a temporary lack of swap space. It is not possible to distinguish this from a failure caused by exceeding
the maximum size of the data segment without consulting getrlimit(2).
BSD
July 12, 1999 BSD