vmfill.c

   1 #include <stdlib.h>
   2 #include <stdint.h>
   3 #include <stdio.h>
   4 #include <sys/mman.h>
   5 #include <fcntl.h>
   6 #include <unistd.h>
   7
   8 #ifndef PAGE_SIZE
   9         #define PAGE_SIZE sysconf(_SC_PAGE_SIZE)
  10 #endif
  11
  12 static void printvm() {
  13         int fd = open("/proc/self/smaps", O_RDONLY);
  14         char buf[4096];
  15         int n;
  16
  17         printf("/proc/self/smaps:\n");
  18         fflush(stdout);
  19         while ((n = read(fd, buf, sizeof buf)) > 0)
  20                 write(1, buf, n);
  21         close(fd);
  22 }
  23
  24 static size_t mmapmax(int fd, void **p) {
  25         size_t i,j,n=0;
  26
  27         for (i=j=SIZE_MAX/2+1; i>=PAGE_SIZE; i/=2) {
  28                 if ((*p=mmap(NULL, j, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED)
  29                         j -= i/2;
  30                 else {
  31                         n = j;
  32                         munmap(*p, n);
  33                         j += i/2;
  34                 }
  35         }
  36         if (n && (*p=mmap(NULL, n, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED) {
  37                 fprintf(stderr, "failed to mmap the same amount again.\n");
  38                 exit(1);
  39         }
  40         return n;
  41 }
  42
  43 int main(int argc, char *argv[]) {
  44         const int fd = open("/dev/zero", O_RDWR);
  45         void *p[100];
  46         size_t n[100];
  47         size_t sum = 0;
  48         int i;
  49         int vmmaps = 0;
  50
  51         if (argc == 2 && argv[1][0]=='-' && argv[1][1]=='v')
  52                 vmmaps = 1;
  53
  54         for (i=0; i<sizeof p/sizeof *p; i++) {
  55                 n[i] = mmapmax(fd, p+i);
  56                 if (!n[i])
  57                         break;
  58                 sum += n[i];
  59                 printf("%d %16zu B %012zx-%012zx\n", i, n[i], (size_t)p[i], (size_t)p[i]+n[i]);
  60         }
  61         printf("mmaped %zu B in %d blocks.\n", sum, i);
  62
  63         printf("try malloc:");
  64         for(i=0; i < 1000 && malloc(PAGE_SIZE) != NULL; i++)
  65                 printf(".");
  66         printf(" %zu B\n", i*(size_t)PAGE_SIZE);
  67
  68         if (vmmaps)
  69                 printvm();
  70         return 0;
  71 }