How to test swap partition

Question

I'm trying to diagnose some random segfaults on a headless server and one thing that seems curious is that they only seem to happen under memory pressure and my swap size will not go above 0.

How can I force my machine to swap to make sure that it is working properly?

orca ~ # free
             total       used       free     shared    buffers     cached
Mem:       1551140    1472392      78748          0     333920    1046368
-/+ buffers/cache:      92104    1459036
Swap:      1060280          0    1060280

orca ~ # swapon -s
Filename                                Type            Size    Used    Priority
/dev/sdb2                               partition       1060280 0       -1

Answer 1

Is this linux? If so you could try the following:

# sysctl vm.swappiness=100

And then either use a program(s) that uses lots of RAM or write a small application that just eats up ram. The following will do that (source: http://www.linuxatemyram.com/play.html):

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

int main(int argc, char** argv) {
    int max = -1;
    int mb = 0;
    char* buffer;

    if(argc > 1)
        max = atoi(argv[1]);

    while((buffer=malloc(1024*1024)) != NULL && mb != max) {
        memset(buffer, 0, 1024*1024);
        mb++;
        printf("Allocated %d MB\n", mb);
        sleep(1);
    }      
return 0;
}

I added the sleep(1) in order to give you more time to watch the processes as it gobbles up ram and swap. The OOM killer should kill this once you are out of RAM and SWAP to give to the program. You can compile it with

gcc filename.c -o memeater

where filename.c is the file you save the above program in. Then you can run it with ./memeater.

I wouldn't do this on a production machine.