/*
 * thrash.c
 *
 * A standalone Unix command-line program to
 * make the machine thrash, ie go into permanent swapping,
 * by using VM >= RAM size and accessing all pages repeatedly
 *
 * Usage: thrash size
 * where "size" is the number of megabytes to thrash
 * A good choice for N is the number of megabytes of physical RAM
 * that the machine has.
 *
 * Reason:
 * to force a machine to use its swap space,
 * to flush all unused pages out to swap and so free RAM for other purposes
 * or to see how a system behaves under extreme duress.
 *
 * It currently *writes* to all pages, but could be made to read them
 * as an alternative, or as well.
 *
 *	Martin Guy, 9 November 2006
 */

#include <stdlib.h>	/* for exit() */
#include <stdio.h>
#include <unistd.h>	/* for system calls */

main(int argc, char **argv)
{
	int megabytes = 0; /* MB of VM to thrash, from command-line argument.
				* 0 means uninitialised */
	char *buf;	/* Huge VM buffer */
	intptr_t bufsize;	/* Size of buffer in bytes */
	long pagesize;	/* size of VM page */
	int i;		/* index into argv */
	int verbose = 0; /* Print a dot for every pass through VM? */

	pagesize = getpagesize();

	for (i=1; i<argc; i++) {
		if (argv[i][0] == '-') {
			switch (argv[i][1]) {
			case 'v': verbose = 1; break;
			default: goto usage;
			}
		} else if (isdigit(argv[i][0])) {
			megabytes = atoi(argv[i]);
			/* Sanity check comes later */
		} else {
usage:			fputs("Usage: thrash [-v] N\n", stderr);
			fputs("-v\tPrint a dot every time for each pass through memoery\n", stderr);
			fputs("N\tNumber of megabytes of VM to thrash\n", stderr);
			exit(1);
		}
	}

	/* Sanity checks */
	if (megabytes <= 0) goto usage;

	bufsize = (long) megabytes * (long)(1024 * 1024);
	buf = (char *) sbrk(bufsize);
	if (buf == (char *)-1) {
		perror("thrash: Failed to allocate VM");
		exit(1);
	}

	/* Write every page repeatedly */
	for (;;) {
		char *p;
		int i;

		for (p=buf, i=bufsize/pagesize; i>0; p+=pagesize, i--)
			*p=(char) i;
		if (verbose) { putchar('.'); fflush(stdout); }
	}
	/* NOTREACHED */
}