Is there a way to kick kswapd and make it swap out pages?

Question

Even though I have set swappiness to 100 and enabled swap, nothing is being swapped out. This is probably because I don't have high memory pressure at the moment. For testing purposes though, I want to force kswapd to swap out as much as it can. Is there a way to kick it into action even though there isn't high memory pressure?

Answer 1

Not that I know of, but you can force it to swap just by allocating (and using) some ram.

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int main(int argc, char **argv)
{
    if (argc < 2)
      return 1;
    int megs = atoi(argv[1]);
    if (megs <= 0)
      return 2;
    int i;
    for (i=0; i<megs; i++) {
        void *data = malloc(1024*1024);
        memset(data, 1, 1024*1024);
    }
    getchar();
    return 0;
}

Save that to eater.c and compiler with gcc -o eater eater.c. (Or whatever your favorite compiler's command line is.) Then simply run that with a number of megabytes as arguments. Hit enter to release it all.

Warning: this will run fast until you actually hit a need for swap. Then your whole system will grind to a halt/start getting OOMs/random apps will start failing if you eat up too much RAM.