threshold_thrasher.c

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>

#include <sys/eventfd.h>

#define USAGE_STR "Usage: cgroup_event_listener <path-to-control-file> <args>"

int main(int argc, char **argv)
{
	int efd = -1;
	int cfd = -1;
	int event_control = -1;
#define PATH_MAX 255
#define LINE_MAX 255
	char event_control_path[PATH_MAX];
	char line[LINE_MAX];
	int ret;
	int blksz_mbs = 20;
	int allocated_mbs = 0;
#define MAXBLOCKS 300
	char *blocks[MAXBLOCKS];
	int index = 0;
	char grow = 1;
	int flags = 0;

	if (argc != 3)
		errx(1, "%s", USAGE_STR);

	cfd = open(argv[1], O_RDONLY);
	if (cfd == -1)
		err(1, "Cannot open %s", argv[1]);

	ret = snprintf(event_control_path, PATH_MAX, "%s/cgroup.event_control",
			dirname(argv[1]));
	if (ret >= PATH_MAX)
		errx(1, "Path to cgroup.event_control is too long");

	event_control = open(event_control_path, O_WRONLY);
	if (event_control == -1)
		err(1, "Cannot open %s", event_control_path);

	efd = eventfd(0, 0);
	if (efd == -1)
		err(1, "eventfd() failed");

	ret = snprintf(line, LINE_MAX, "%d %d %s", efd, cfd, argv[2]);
	if (ret >= LINE_MAX)
		errx(1, "Arguments string is too long");

	ret = write(event_control, line, strlen(line) + 1);
	if (ret == -1)
		err(1, "Cannot write to cgroup.event_control");

	flags = fcntl(efd, F_GETFL, 0);
	ret = fcntl(efd, F_SETFL, flags | O_NONBLOCK);
	if (ret == -1)
		err(1, "Cannot set non-blocking read");

#define PAGESIZE 4096
	while (1) {
		uint64_t result;
		char *mem;

		if (grow) {
			// allocate more memory to try to hit threshold
			if (index >= MAXBLOCKS)
				err(1, "maximum allowed sized reached without hitting threshold");
			mem = (char *)malloc(blksz_mbs<<20);
			if (!mem)
				err(1, "failed to allocate memory");
			blocks[index++] = mem;
			allocated_mbs += blksz_mbs;

			/* touch each page to force actual allocation */
			for (int i = 0; i < blksz_mbs<<20 ; i += PAGESIZE) {
				memset(mem + i, 0, 1);
			}
			printf("allocated\n");
		} else {
			// free memory to drop below threshold
			if (index <= 0)
				err(1, "no blocks left to free to get below threshold");
			free(blocks[--index]);
			allocated_mbs -= blksz_mbs;
			usleep(100000);
			printf("freed\n");
		}

		ret = read(efd, &result, sizeof(result));
		if (ret == -1) {
			if (errno == EINTR)
				continue;
			if (errno == EAGAIN) {
				printf("not at threshold yet. %d MB allocated.\n", allocated_mbs);
				continue;
			}
			err(1, "Cannot read from eventfd");
		}
		assert(ret == sizeof(result));

		printf("%s %s: crossed\n", argv[1], argv[2]);
		grow = !grow;
	}

	return 0;
}