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

/*
 * This program allocates physical memory and holds it.  Its primary purpose is to 
 * reduce the available memory on the machine in order to test how other programs
 * deal with low memory conditions.
 *
 * The mmap call creates the memory regions, and mlock locks the memory pages to physical
 * RAM.  Memory is allocated into small pieces to make sure that we don't have trouble
 * with address space fragmentation.
 */
                                  
/* 64mb allocation size */
#define CHUNK_SIZE   (1024*1024*64)                      

int main( int argc, char** argv ) { 
    if( argc < 2 ) {
        fprintf( stderr, "You need to specify an amount of memory, in megabytes.\n" );
    }                    
    
    size_t length = atol( argv[1] );
    length *= 1024 * 1024;  
    int result;
    size_t chunk;
    void* mapping;          
    
    while( length > 0 ) {
        if( CHUNK_SIZE < length ) {
            chunk = CHUNK_SIZE;
        } else {                   
            chunk = length;
        }                      
        
        mapping = mmap( 0, chunk, PROT_WRITE | PROT_READ, MAP_ANON | MAP_SHARED, 0, 0 );
        
        if( mapping == (void*)-1 )
            perror( "Couldn't map some of the memory." );      
            
        result = mlock( mapping, chunk );      
        
        if( result < 0 )
            perror( "Couldn't lock some pages." );
               
        printf( "# %zdMB (%zdMB left)\n", chunk / (1024*1024), (length - chunk) / (1024*1024) );
        fflush(stdout);
        length -= chunk;
    }                       
                      
    printf( "Memory locked.\n" );    
    // wait for someone to kill the process  
    while (1)
        sleep(1000); 
}