[PATCH 0/2] hugetlb fixes

[Joern Engel <joern@logfs.org>]

As everyone knows, hugetlbfs sucks.  But it is also necessary for
large memory machines, so we should make it suck less.  Top of my list
were lack of rss accounting and refusing mmap with MAP_HUGETLB when
using hugetlbfs.  The latter generally created a know in every brain I
explained this to.

Test program below is failing before these two patches and passing
after.

Joern Engel (2):
  hugetlb: properly account rss
  mmap: allow MAP_HUGETLB for hugetlbfs files

 mm/hugetlb.c |    4 ++++
 mm/mmap.c    |   12 ++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

-- 
1.7.10.4

#define _GNU_SOURCE
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

typedef unsigned long long u64;

static size_t length = 1 << 24;

static u64 read_rss(void)
{
	char buf[4096], *s = buf;
	int i, fd;
	u64 rss;

	fd = open("/proc/self/statm", O_RDONLY);
	assert(fd > 2);
	memset(buf, 0, sizeof(buf));
	read(fd, buf, sizeof(buf) - 1);
	for (i = 0; i < 1; i++)
		s = strchr(s, ' ') + 1;
	rss = strtoull(s, NULL, 10);
	return rss << 12; /* assumes 4k pagesize */
}

static void do_mmap(int fd, int extra_flags, int unmap)
{
	int *p;
	int flags = MAP_PRIVATE | MAP_POPULATE | extra_flags;
	u64 before, after;

	before = read_rss();
	p = mmap(NULL, length, PROT_READ | PROT_WRITE, flags, fd, 0);
	assert(p != MAP_FAILED ||
			!"mmap returned an unexpected error");
	after = read_rss();
	assert(llabs(after - before - length) < 0x40000 ||
			!"rss didn't grow as expected");
	if (!unmap)
		return;
	munmap(p, length);
	after = read_rss();
	assert(llabs(after - before) < 0x40000 ||
			!"rss didn't shrink as expected");
}

static int open_file(const char *path)
{
	int fd, err;

	unlink(path);
	fd = open(path, O_CREAT | O_RDWR | O_TRUNC | O_EXCL
			| O_LARGEFILE | O_CLOEXEC, 0600);
	assert(fd > 2);
	unlink(path);
	err = ftruncate(fd, length);
	assert(!err);
	return fd;
}

int main(void)
{
	int hugefd, fd;

	fd = open_file("/dev/shm/hugetlbhog");
	hugefd = open_file("/hugepages/hugetlbhog");

	system("echo 100 > /proc/sys/vm/nr_hugepages");
	do_mmap(-1, MAP_ANONYMOUS, 1);
	do_mmap(fd, 0, 1);
	do_mmap(-1, MAP_ANONYMOUS | MAP_HUGETLB, 1);
	do_mmap(hugefd, 0, 1);
	do_mmap(hugefd, MAP_HUGETLB, 1);
	/* Leak the last one to test do_exit() */
	do_mmap(-1, MAP_ANONYMOUS | MAP_HUGETLB, 0);
	printf("oll korrekt.\n");
	return 0;
}

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>