C Program on Linux to exhaust memory

Question

I would like to write a program to consume all the memory available to understand the outcome. I've heard that linux starts killing the processes once it is unable to allocate the memory.

Can anyone help me with such a program.

I have written the following, but the memory doesn't seem to get exhausted:

#include <stdlib.h>  int main() {         while(1)         {                 malloc(1024*1024);         }         return 0; } 

Answer 1

You should write to the allocated blocks. If you just ask for memory, linux might just hand out a reservation for memory, but nothing will be allocated until the memory is accessed.

int main() {         while(1)         {                 void *m = malloc(1024*1024);                 memset(m,0,1024*1024);         }         return 0; } 

You really only need to write 1 byte on every page (4096 bytes on x86 normally) though.

Answer 2

Linux "over commits" memory. This means that physical memory is only given to a process when the process first tries to access it, not when the malloc is first executed. To disable this behavior, do the following (as root):

echo 2 > /proc/sys/vm/overcommit_memory 

Then try running your program.