02-17-2006
The system calls brk() or sbrk() on behalf of the process to get chunks of memory.
As the program runs and requests more memory, the system calls for more.
Generally, this memory accumulates, with the idea that since the processes needed it before, it may well need it again. Calling brk() & sbrk() is expensive.
The simple way to see a memory leak is have the code run for longer periods. If memory continually grows, then there is probably problem.
If you need to find the leak - try either Electric Fence or Valgrind.
They are available free, and have been ported to most versions of UNIX.
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BRK(2) Linux Programmer's Manual BRK(2)
NAME
brk, sbrk - change data segment size
SYNOPSIS
#include <unistd.h>
int brk(void *addr);
void *sbrk(intptr_t increment);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
brk(), sbrk():
Since glibc 2.19:
_DEFAULT_SOURCE ||
(_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L)
From glibc 2.12 to 2.19:
_BSD_SOURCE || _SVID_SOURCE ||
(_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L)
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
DESCRIPTION
brk() and sbrk() change the location of the program break, which defines the end of the process's data segment (i.e., the program break is
the first location after the end of the uninitialized data segment). Increasing the program break has the effect of allocating memory to
the process; decreasing the break deallocates memory.
brk() sets the end of the data segment to the value specified by addr, when that value is reasonable, the system has enough memory, and the
process does not exceed its maximum data size (see setrlimit(2)).
sbrk() increments the program's data space by increment bytes. Calling sbrk() with an increment of 0 can be used to find the current loca-
tion of the program break.
RETURN VALUE
On success, brk() returns zero. On error, -1 is returned, and errno is set to ENOMEM.
On success, sbrk() returns the previous program break. (If the break was increased, then this value is a pointer to the start of the newly
allocated memory). On error, (void *) -1 is returned, and errno is set to ENOMEM.
CONFORMING TO
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
NOTES
Avoid using brk() and sbrk(): the malloc(3) memory allocation package is the portable and comfortable way of allocating memory.
Various systems use various types for the argument of sbrk(). Common are int, ssize_t, ptrdiff_t, intptr_t.
C library/kernel differences
The return value described above for brk() is the behavior provided by the glibc wrapper function for the Linux brk() system call. (On
most other implementations, the return value from brk() is the same; this return value was also specified in SUSv2.) However, the actual
Linux system call returns the new program break on success. On failure, the system call returns the current break. The glibc wrapper
function does some work (i.e., checks whether the new break is less than addr) to provide the 0 and -1 return values described above.
On Linux, sbrk() is implemented as a library function that uses the brk() system call, and does some internal bookkeeping so that it can
return the old break value.
SEE ALSO
execve(2), getrlimit(2), end(3), malloc(3)
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2016-03-15 BRK(2)