Date: Wed, 05 Jun 2002 23:56:57 -0500 From: Stephen Montgomery-Smith <stephen@math.missouri.edu> To: freebsd-hackers@freebsd.org Subject: allocating memory Message-ID: <3CFEEB99.AEDC5DB9@math.missouri.edu>
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I have access to a rather large computer (3GB of RAM) and I would like
to write a program to access most of this memory. I find that I am
unable to malloc more than about 0.5 GB of memory, even if I do it in
small increments. Now I am trying mmap, and this lets me get to about
2.5 GB of memory (again I ask for the memory in small increments). What
is it that causes these limitations?
Here is the kind of program I used to find these limits:
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/mman.h>
#define size 100000000
#define nr 100
main() {
char *a[nr];
unsigned int i, j;
for (j=0;j<nr;j++) {
fprintf(stderr,"Mallocing a[%d] with %d bytes\n",j,size);
a[j] =
mmap(NULL,size,PROT_READ|PROT_WRITE,MAP_ANON|MAP_NOCORE,-1,0);
fprintf(stderr,"%d\n",(int)(a[j]));
if (a[j]==MAP_FAILED) {
perror("malloc error");
exit(EXIT_FAILURE);
}
fprintf(stderr,"Filling a[%d]\n",j);
for(i=0;i<size;i++) a[j][i] = i;
fprintf(stderr,"Done\n");
}
while(1){} /* so the program doesn't stop and stays at the top of top
*/
}
--
Stephen Montgomery-Smith
stephen@math.missouri.edu
http://www.math.missouri.edu/~stephen
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