hugetlbfs-reserve-with-fd.c

#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE

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

#include <errno.h>
#include <sys/mman.h>
#include <unistd.h>

#define HPAGE_SIZE	(16 * 1024 * 1024ULL)
#define MAP_LENGTH	(2 * HPAGE_SIZE)

#define HPAGE_BASE_FMT	"/sys/kernel/mm/hugepages/hugepages-%lukB/"
#define HPAGE_FREE_FMT	HPAGE_BASE_FMT "free_hugepages"
#define HPAGE_RESV_FMT	HPAGE_BASE_FMT "resv_hugepages"

unsigned long read_ulong_from_file(char *filename)
{
	unsigned long val;
	FILE *fp;

	fp = fopen(filename, "r");
	if (!fp) {
		fprintf(stderr, "fopen(): %s\n", strerror(errno));
		exit(EXIT_FAILURE);
	}

	fscanf(fp, "%lu", &val);
	fclose(fp);

	return val;
}

void print_hpage_stats(unsigned long pgsize)
{
	unsigned long free, resv, pgsizekb;
	char filename[128];

	fflush(stdout);
	pgsizekb = pgsize / 1024;

	/* Read count of free huge pages */
	sprintf(filename, HPAGE_FREE_FMT, pgsizekb);
	free = read_ulong_from_file(filename);

	/* Read count of reserved huge pages */
	sprintf(filename, HPAGE_RESV_FMT, pgsizekb);
	resv = read_ulong_from_file(filename);

	printf("stats: free = %lu, resv = %lu\n", free, resv);
}

int get_hugetlbfs_subpool_fd(void)
{
	const char *path = "/var/lib/hugetlbfs/global/pagesize-16MB";
	// const char *path = "/home/sandipan/hugemount";
	char name[64];
	int fd;

	/* Build temporary file name template */
	strcpy(name, path);
	strncat(name, "/libhugetlbfs.tmp.XXXXXX", sizeof(name) - 1);

	/* Create temporary file */
	fd = mkstemp64(name);

	if (fd < 0) {
		fprintf(stderr, "mkstemp(): %s\n", strerror(errno));
		exit(EXIT_FAILURE);
	}

	/* Unlink file */
	unlink(name);
	return fd;
}

void print_proc_maps(void)
{
	const char *fmt = "cat /proc/%u/maps";
	char cmd[128];

	sprintf(cmd, fmt, (unsigned int) getpid());
	system(cmd);
}

int main(int argc, char **argv)
{
	void *ptr;
	int fd;

	fd = get_hugetlbfs_subpool_fd();

	printf("pre-mmap: ");
	print_hpage_stats(HPAGE_SIZE);

	/* Allocate a huge page */
	ptr = mmap(NULL, MAP_LENGTH, PROT_READ | PROT_WRITE,
		   MAP_PRIVATE, fd, 0);
	if (ptr == MAP_FAILED) {
		fprintf(stderr, "mmap(): %s\n", strerror(errno));
		return EXIT_FAILURE;
	}

	printf("post-mmap, pre-fault: ");
	print_hpage_stats(HPAGE_SIZE);
	getchar();

	/* Attempt to generate a page fault */
	printf("mmap-ed base = 0x%016lx\n", (unsigned long) ptr);
	((char *) ptr)[0] = 0xff;
	((char *) ptr)[HPAGE_SIZE] = 0xff;

	printf("post-fault: ");
	print_hpage_stats(HPAGE_SIZE);
	print_proc_maps();
	getchar();

	/* Free up the huge page */
	if (munmap(ptr, MAP_LENGTH) < 0) {
		fprintf(stderr, "munmap(): %s\n", strerror(errno));
		return EXIT_FAILURE;
	}

	close(fd);
	return EXIT_SUCCESS;
}