Bug 679021

Description of problem:
The global nr_mapped count in /proc/vmstat represents all mapped file pages, whereas mapped_file in /cgroup/memory/memory.stat does not include shmem pages.

How reproducible:
The counters differ by the number of shmem pages, so creating those makes the problem visible.

Steps to Reproduce:
compare the counters before and after creating a few thousand shmem pages

# cat /cgroup/memory/memory.stat /proc/vmstat | awk '/^mapped_file/ { print($2 / 4096); } /^nr_mapped/ { print $2 }'
# ./mkshmem &
# !-2
  
Actual results:
The counters differ by roughly the number of shmem pages mkshmem created.

Expected results:
The counters should be roughly the same.

Additional info:

/* gcc -o mkshmem mkshmem.c */

#include <sys/mman.h>
#include <string.h>
#include <stdio.h>

#define SIZE    (20UL << 20)

int main(void)
{
        char *map;

        map = mmap(NULL, SIZE, PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
        if (map == MAP_FAILED)
                return 1;
        memset(map, 0, SIZE);
        getchar();
        munmap(map, SIZE);
        return 0;
}