/*
sp_tester.c

Build with:
gcc -o sp_tester sp_tester.c -lrt -W -Wall -O2

How to use:
echo 1 > /proc/sys/vm/overcommit_memory
swapoff -a
swapon -a
./sp_tester

then repeat with changed conditions eg
echo 0 > /proc/sys/vm/swap_prefetch

Each Test takes 10 minutes
*/

#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <time.h>

void fatal(const char *format, ...)
{
	va_list ap;

	if (format) {
		va_start(ap, format);
		vfprintf(stderr, format, ap);
		va_end(ap);
	}

	fprintf(stderr, "Fatal error - exiting\n");
	exit(1);
}

unsigned long ramsize, swapsize;

size_t get_ram(void)
{
	FILE *meminfo;
        char aux[256];

	if(!(meminfo = fopen("/proc/meminfo", "r")))
		fatal("fopen\n");

	while( !feof(meminfo) && !fscanf(meminfo, "MemTotal: %lu kB", &ramsize) )
		fgets(aux,sizeof(aux),meminfo);
	while( !feof(meminfo) && !fscanf(meminfo, "SwapTotal: %lu kB", &swapsize) )
		fgets(aux,sizeof(aux),meminfo);
	if (fclose(meminfo) == -1)
		fatal("fclose");
	ramsize *= 1000;
	swapsize *= 1000;
	printf("Ram %lu  Swap %lu\n", ramsize, swapsize);
	return ramsize + (swapsize / 2);
}

unsigned long get_usecs(struct timespec *myts)
{
	if (clock_gettime(CLOCK_REALTIME, myts))
		fatal("clock_gettime");
	return (myts->tv_sec * 1000000 + myts->tv_nsec / 1000 );
}

int main(void)
{
	unsigned long current_time, time_diff;
	struct timespec myts;
	char *buf1, *buf2, *buf3, *buf4;
	size_t size = get_ram();
	int sleep_seconds = 600;

	if (size > ramsize / 2 * 3)
		size = ramsize / 2 * 3;
	printf("Total ram to be malloced: %u bytes\n", size);
	size /= 2;
	printf("Starting first malloc of %u bytes\n", size);
	buf1 = malloc(size);
	buf4 = malloc(1);
	if (buf1 == (char *)-1)
		fatal("Failed to malloc 1st buffer\n");
	memset(buf1, 0, size);
	time_diff = current_time = get_usecs(&myts);
	for (buf3 = buf1; buf3 < buf1 + size; buf3++)
		*buf4 = *buf3;
	printf("Starting 1st read of first malloc\n");
	current_time = get_usecs(&myts);
	time_diff = current_time - time_diff;
	printf("Touching this much ram takes %lu milliseconds\n",time_diff / 1000);
	printf("Starting second malloc of %u bytes\n", size);

	buf2 = malloc(size);
	if (buf2 == (char *)-1)
		fatal("Failed to malloc 2nd buffer\n");
	memset(buf2, 0, size);
	for (buf3 = buf2 + size; buf3 > buf2; buf3--)
		*buf4 = *buf3;
	free(buf2);
	printf("Completed second malloc and free\n");

	printf("Sleeping for %u seconds\n", sleep_seconds);
	sleep(sleep_seconds);

	printf("Important part - starting reread of first malloc\n");
	time_diff = current_time = get_usecs(&myts);
	for (buf3 = buf1; buf3 < buf1 + size; buf3++)
		*buf4 = *buf3;
	current_time = get_usecs(&myts);
	time_diff = current_time - time_diff;
	printf("Completed read of first malloc\n");
	printf("Timed portion %lu milliseconds\n",time_diff / 1000);

	free(buf1);
	free(buf4);

	return 0;
}