gistfile1.c

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

static struct chunk {
  struct chunk *next;
  uint32_t base;
  uint32_t len;
} *clist;

static int n_mmap, n_munmap;

#define LIMIT (1024 * 1024)

static void reserve(uint32_t base, uint64_t len)
{
  void *p;
  struct chunk *c;
  if (len < LIMIT) return;
  p = mmap((void*)(uintptr_t)base, len, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  n_mmap++;
  if (p == MAP_FAILED || p != (void*)(uintptr_t)base) {
    struct chunk *c1, *c2;
    if (p != MAP_FAILED) {
      n_munmap++;
      munmap(p, len);
    }
    reserve(base, len / 2);
    reserve(base + len / 2, len / 2);
    return;
  }
  c = malloc(sizeof(*c));
  c->base = base;
  c->len = len;
  c->next = clist;
  clist = c;
}

int main()
{
  uint64_t total = 0;
  struct chunk *c;
  reserve(0,0x100000000);
  for (c = clist; c; c = c->next) {
    printf("Chunk 0x%08llx - 0x%08llx, len %u MB\n", c->base, (uint64_t)c->base + c->len, c->len >> 20);
    total += c->len;
  }
  printf("Seized total of %lu MB using %dx mmap, %dx munmap\n", total >> 20, n_mmap, n_munmap);
}