Linux hugepage alloc demo1
Posted by Anonymous on Tue 6th Sep 2022 14:06
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/*
 * hugepage_alloc_test1.c - test the availabilty of hugepages
 *
 * Written by Roland Mainz <roland.mainz@nrubsig.org>
 */

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

#include <sys/mman.h>
#include <sys/stat.h>

#include <linux/mman.h>

/*
 * Before using this Linux 5.10.0-13-rt-686-pae requires that "root"
 * reserves hugepages like this:
 *
 * $ printf '128' > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
 * $ cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
 * 128
 *
 * Notes:
 * - Terminology: UNIX uses the term "largepages", Linux defiantly uses
 * "hugepages"
 * - the value is the number of MMU (large-/huge-)pages, NOT the number
 * of bytes.
 * - $ /usr/bin/pagesize -a # can inform you which pagesizes are
 * available (i686 usually has { 4k, 2M } pagesizes, SPARCv9 has
 * { 8k, 64k, 4M, 32M, ... } )
 */

ssize_t get_number_of_free_hugepages(void)
{
        int     dirfd;
        int     fd;
        char    buf[256];
        ssize_t numpages;
        ssize_t rs; /* read size */

        /*
         * extra step here, since real-world applications likely
         * want to look at "nr_hugepages" etc, too
         */
        dirfd = open("/sys/kernel/mm/hugepages/hugepages-2048kB/",
                O_DIRECTORY);
        if (dirfd < 0) {
                perror("open sysfs hugepage dir");
                return -1;
        }

        fd = openat(dirfd, "free_hugepages", O_RDONLY);
        if (fd < 0) {
                perror("open sysfs hugepage free pages file");
                (void)close(dirfd);
                return -1;
        }
        rs = read(fd, buf, sizeof(buf));
        if (rs < 0) {
                perror("read error sysfs hugepage free pages file");
                (void)close(dirfd);
                (void)close(fd);
                return -1;
        }

        (void)close(dirfd);
        (void)close(fd);

        buf[rs] = '\0';
#if MYDEBUG
        if ((rs > 0) && (buf[rs-1] == '\n'))
                buf[rs-1] = '\0';
        (void)printf("string returned: |%s|\n", buf);
#endif /* MYDEBUG */

        errno = 0;
        numpages = strtol(buf, NULL, 10);
        if (errno != 0) {
                perror("error parsing value of free hugepages");
                return -1;
        }

        return numpages;
}


int main(int ac, char *av[])
{
        void *p;
        int saved_errno;
#define TEST_NUM_ALLOC_PAGES (32)
        size_t size = TEST_NUM_ALLOC_PAGES*1024*1024;
        ssize_t free_numpages;

        (void)puts("#start.");

        free_numpages = get_number_of_free_hugepages();

        if (free_numpages < (TEST_NUM_ALLOC_PAGES+8)) {
                fprintf(stderr, "not enough hugepages\n");
                return EXIT_FAILURE;
        }

        p = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB, -1, 0);
        saved_errno = errno;
        if (p == MAP_FAILED)
                perror("mmap");

        (void)printf("map address = %lx, errno=%d\n",
                (unsigned long)p, (int)saved_errno);

        if (munmap(p, size) == -1)
                perror("munmap");

        (void)puts("#done.");

        return EXIT_SUCCESS;
}