11-05-2008
Your assumption seems wrong to me.
First off, Shamrock showed you how to get address space there is for a process versus how much "physical" virtual space is available through hardware and disk files.
The "hardware" part is OS dependent. Your assumption is that somehow the system reserves virtual space for each process. NO. It does not. The system gives memory space via sbrk() or brk() calls to any process requesting it. brk() fails when there is no more virtual space to be had. sbrk() returns SBRK_FAILED and brk() returns -1 on failure.
If the system "set aside" memory ahead of time, then these calls would not be needed.
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
Hello,
Please help me to know, How to find out the how much amount of process addres space is required/is used for/by a process.
Tnx & Regards
Vishwa. (1 Reply)
Discussion started by: S.Vishwanath
1 Replies
2. Programming
Hi,
In Linux how to find out what will be the stack size allocated for a process?
Actually i have to fork n number of processess, and will call exec. I will be execing an executable which is already multithreaded and each thread size is defined. My doubt is how to know if the size of the... (2 Replies)
Discussion started by: rvan
2 Replies
3. UNIX for Dummies Questions & Answers
Hello all
im using the ps -ef "args vsz" | some.exe
but the result is in kb , is there some kind of way or flag ( didnt found in the ps man )
to convert me this data to GB or MG in human readable format ?
Thanks (1 Reply)
Discussion started by: umen
1 Replies
4. Shell Programming and Scripting
Hello
i am working on a project here is part of script that i need a help in
get process SpectroSERVER current size if it exceed 3850 MB then
#pkill -TERM ArchMgr
and wait to succfull shutdown message from the log file to proceed to the next step
#tail -f $SPECROOT/SS/DDM/ARCHMGR.OUT... (7 Replies)
Discussion started by: mogabr
7 Replies
5. UNIX for Advanced & Expert Users
Can kernel process access user address space ? (2 Replies)
Discussion started by: subhotech
2 Replies
6. Programming
Hi All,
From C++, I just want to find the address space size that a process is allowed to use. For ex, in 32 bit OS the allowed address space is 4GB and in 64 bit OS I guess this is 16GB or more.
I jsut want to find it in my C++ project. Is there any API calls that gives me such information.... (2 Replies)
Discussion started by: Sendil Kumar
2 Replies
7. UNIX for Advanced & Expert Users
Hello all,
To do a self-exec or self-restart of a process when it crosses the threshold memory limit, I use the value of virtual memory size field from /proc/$pid/stat file and do a self-exec.
According to man 5 proc
vsize %lu
Virtual memory size in bytes.
I just want to... (2 Replies)
Discussion started by: matrixmadhan
2 Replies
8. UNIX for Dummies Questions & Answers
Hi guys,
I got one problem which I definetily no idea.
What would the physical address be for virtual address?
1) 2ABC
2) 3F4B
Here is the page table:see attached
Thank you sos sososososso much!! (0 Replies)
Discussion started by: lemon_06
0 Replies
9. Programming
Suppose I have 3 gb of ram and 250 gb hard disk in my pc.
Now I wrote a simple C program having only one statement malloc() to allocate 4 gb of memory as 32 bit os can address 4gb address space then will the malloc succeed?
If yes then how it will get extra 1 gb of memory?
Does the process gets... (3 Replies)
Discussion started by: rupeshkp728
3 Replies
10. Programming
Hello all
i have simple server running on linux redhat 6.1
it is build with c++
in the server i have huge std vector that holds pointers to cache objects
those cache objects holds allot of data from the DB
any way ...
in some point in time there is simple API that suppose to clean the... (2 Replies)
Discussion started by: umen
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 <unistd.h>
int
brk(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'').
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 brk() function sets the break to addr.
The sbrk() function raises the break by at least incr bytes, thus allocating at least incr bytes of new memory in the data segment. If incr
is negative, the break is lowered by incr bytes.
sbrk() returns the prior address of the break. 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 the RLIMIT_DATA rlim_max value returned from a call to getrlimit(2), e.g. ``etext + rlim.rlim_max''. (see end(3) for the defi-
nition of etext).
RETURN VALUES
brk() returns 0 if successful; otherwise -1 with errno set to indicate why the allocation failed.
The sbrk() function returns the prior break value if successful; otherwise ((void *)-1) is returned and errno is set to indicate why the
allocation failed.
ERRORS
brk() or sbrk() will fail and no additional memory will be allocated if one of the following are true:
[ENOMEM] The limit, as set by setrlimit(2), was exceeded.
[ENOMEM] The maximum possible size of a data segment (compiled into the system) was exceeded.
[ENOMEM] Insufficient space existed in the swap area to support the expansion.
SEE ALSO
execve(2), getrlimit(2), mmap(2), end(3), free(3), malloc(3), sysconf(3)
HISTORY
A brk() function call appeared in Version 7 AT&T UNIX.
BUGS
Note that mixing brk() and sbrk() with malloc(3), free(3), and similar functions may result in non-portable program behavior. Caution is
advised.
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