this is test program:
#include <stdio.h>
#include <stdlib.h>

int main( int argc, char **argv )
{
    #define MAX_NO 20
    #define MAX_TIME 50
    char *pt[MAX_NO], *tmp;
    size_t i, j, k, size_len[MAX_NO], size_add;
    
    
    for( i=0; i<100000; i++ )
    {
        for( j=0; j<MAX_NO; j++ )
        {
            size_add = rand();
            size_add %= 100000;    //  limit add size
            size_len[j] = 1920520 + size_add;
            pt[j] = (char*)malloc( size_len[j] );
        }
        for( k=0; k<MAX_TIME; k++ )
        {
            for( j=0; j<MAX_NO; j++ )
            {
                if( pt[j] != NULL )
                {
                    size_add = rand();
                    size_add %= 100000;    //  limit add size
                    tmp = pt[j];
                    size_len[j] += size_add;
                    tmp = (char*)realloc( tmp, size_len[j] );
                    if( tmp != NULL )
                    {
                        pt[j] = tmp;
                    }
                    else
                        printf( "realloc() fail\n" );
                }
            }
        }
        for( j=0; j<MAX_NO; j++ )
        {
            if( pt[j] != NULL )
                free( pt[j] );
        }
    }
    return 0;
}
====================================
this is result running by valgrind:
top - 12:37:25 up 101 days, 19:29,  2 users,  load average: 1.74, 1.53, 0.94
Tasks:  56 total,   2 running,  53 sleeping,   1 stopped,   0 zombie
Cpu(s): 44.3% us,  6.3% sy,  0.0% ni,  0.0% id, 48.7% wa,  0.7% hi,  0.0% si
Mem:    507796k total,   502548k used,     5248k free,      400k buffers
Swap:  1020116k total,    52392k used,   967724k free,     6272k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
31561 fisherw   18   0 1770m 454m  860 R 49.6 91.6   0:09.39 valgrind
                                              ====   
================================
this is result running without valgrind:
top - 12:36:34 up 101 days, 19:28,  2 users,  load average: 2.65, 1.62, 0.93
Tasks:  56 total,   3 running,  52 sleeping,   1 stopped,   0 zombie
Cpu(s):  9.0% us, 91.0% sy,  0.0% ni,  0.0% id,  0.0% wa,  0.0% hi,  0.0% si
Mem:    507796k total,    93308k used,   414488k free,      884k buffers
Swap:  1020116k total,    60544k used,   959572k free,    13892k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
31454 fisherw   25   0 72752  388  256 R 99.9  0.1   0:14.81 realloc
                                               ===