Resident memory is growing huge as I do memset in a for loop

[ArunSL]

Hello All,

I am having a tricky issue here.

I wanted to limit the resident memory usage of processes and to test it out I wrote a program that allocates memory and write some data using memset.

It was found that If I do not use memset, the program runs OK, resident memory usage of the program is within lower limits, and virtual memory grows up as expected. But If I use memset, the resident memory is growing till a point where the whole of memory is used up and eventually resulting in a crash.

Compile and run the following program and observe top for the memory usage of the program

The simple program is as follows:


#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int main()
{
char *memTest;
int i;
for(i =0; i<100; i++)
{
memTest = calloc(5000000000,sizeof(memTest));
// If I comment the following line resident memory is not growing
memset(memTest,9,5000000000);
printf("\nItteration: %d",i);
sleep(1);
}
return 0;
}


The question that is really bothering me here is that why kernel is not freeing up resident memory when it is not in use? Some page out operation that was due is not happening.

The OS used is SUSE 11.2, but guess this is a Linux kernel issue and not OS specific.

Any help is appreciated.

\\ Regards,

ArunSL

[Rubberman]

You keep allocating data, but you never free it. Try this instead:

int main()
{
    char *memTest;
    int i;
    for(i =0; i<100; i++) 
    {
        memTest = calloc(5000000000,sizeof(memTest));
       // If I comment the following line resident memory is not growing
       memset(memTest,9,5000000000);
       printf("\nItteration: %d",i);
       free(memTest);
       sleep(1);
    }
    return 0;
}