mlock() is working?

mlock() is working?

[Tiago Vignatti]

Hi guys,

I'm trying to lock some piece of the code in memory using mlock(). I did 
a simple program to test it and to certify I using my own simple page 
fault notifier [0]. The program is below.

-- cut --

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

#define SIZE 10000

int mlock_all = 0;

int
f(void)
{
     int c[SIZE];
     int i;

     if (mlock_all) {
         if (!mlockall(MCL_CURRENT))
             fprintf(stderr, "mlockall'ed succefully\n");
         else
             perror("mlockall");
     }
     else {
         if (!mlock(&c[0], SIZE))
             fprintf(stderr, "mlock'ed succefully\n");
         else
             perror("mlock");
     }

     fprintf(stderr, "start: 0x%x, end: 0x%x\n", &c[0], &c[SIZE]);

     for (i = 0; i < SIZE; i++)
         c[i] = i;

}
int
main(int argc, char **argv)
{
     if (argv[1])
         mlock_all = 1;

     while(1) {
         f();
         sleep (15);
     }

     return 0;
}

-- cut --


So, if I use mlockall() I always obtained the desired result, i.e., I 
lock the 'c[SIZE]'. But when I switch to mlock() it never works and my 
page fault notifier prints all pages concerning 'c[SIZE]'. Am I missing 
something? Is it possible to lock the automatic variables?

My Linux is 2.6.22.2.

my regards

[0] http://lkml.org/lkml/2007/7/27/11
     http://lkml.org/lkml/2007/7/27/8

-- 
Tiago Vignatti
C3SL - Centro de Computação Científica e Software Livre
www.c3sl.ufpr.br