[BUG] mlocked page counter mismatch

MinChan Kim
2009-01-28T10:28:56Z

After executing following program, 'cat /proc/meminfo' shows
following result.

--
# cat /proc/meminfo
..
Unevictable: 8 kB
Mlocked: 8 kB
..

-- test program --

#include <stdio.h>
#include <sys/mman.h>
int main()
{
char buf[64] = {0,};
char *ptr;
int k;
int i,j;
int x,y;
mlockall(MCL_CURRENT);
sprintf(buf, "cat /proc/%d/maps", getpid());
system(buf);
return 0;
}

--

It seems mlocked page counter have a problem.
After I diged in source, I found that try_to_unmap_file called
try_to_mlock_page about shared mapping pages
since other vma had VM_LOCKED flag.
After all, try_to_mlock_page called mlock_vma_page.
so, mlocked counter increased

But, After I called munlockall intentionally, the counter work well.
In case of munlockall, we already had a mmap_sem about write.
Such a case, try_to_mlock_page can't call mlock_vma_page.
so, mlocked counter didn't increased.
As a result, the counter seems to be work well but I think
it also have a problem.