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Subjectmmap'ing a large file
Date
Is there a logical reason why a process can't mmap more than a 2G file?

I seem to get stuck at 2142208000 with
mmap: Cannot allocate memory

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define FILESIZE 2500000000

int
main ()
{
unsigned long long offset = 0;
unsigned long maplength = getpagesize () * 1000;
int i;
unsigned char *p;
char mynull = 0;
int fd = open ("test.map", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
if (fd < 0) {
perror ("test.map");
exit (-1);
}
lseek (fd, FILESIZE - 1, SEEK_SET);
write (fd, &mynull, 1);
for (offset = 0; offset < FILESIZE - maplength; offset += maplength) {
p = mmap (p, maplength, PROT_READ | PROT_WRITE, MAP_SHARED, fd,offset);
printf ("%lld %p\n", offset, p);
fflush (stdout);
if (p == (unsigned char *) -1) {
perror ("mmap");
exit (-1);
}
memset (p, 1, maplength);
#if 0
munmap (p, maplength); /* this of course let's things go on */
#endif
}
return 0;
}


Michael D. Black mblack@csi-inc.com
http://www.csi-inc.com/
http://www.csi-inc.com/~mike
321-676-2923, x203
Melbourne FL

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