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 alloc

Answer 1

In my machine, with an appropriate gb value, the following code used 100% of the memory, and even got memory into the swap. You can see that you need to write only one byte in each page: memset(m, 0, 1);, If you change the page size: #define PAGE_SZ (1<<12) to a bigger page size: #define PAGE_SZ (1<<13) then you won't be writing to all the pages you allocated, thus you can see in top that the memory consumption of the program goes down.

#include 
#include 
#include 

#define PAGE_SZ (1<<12)

int main() {
    int i;
    int gb = 2; // memory to consume in GB

    for (i = 0; i < ((unsigned long)gb<<30)/PAGE_SZ ; ++i) {
        void *m = malloc(PAGE_SZ);
        if (!m)
            break;
        memset(m, 0, 1);
    }
    printf("allocated %lu MB\n", ((unsigned long)i*PAGE_SZ)>>20);
    getchar();
    return 0;
}