mmap_max

virtual_memory_limit.c

#include <memory.h>
#define _XOPEN_SOURCE_EXTENDED 1
#include <sys/mman.h>
#include <stdint.h>
#include <stdio.h>
#include <climits>
#include <algorithm>

int main() {
  int flags = MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE;
  int prot = PROT_READ | PROT_WRITE;

  int64_t ok = 0;
  int64_t ng = INT64_MAX;
  while (std::abs(ng - ok) > 1) {
    uint64_t mid = (ok + ng) / 2;

    uint64_t vmsize = mid;
    void* virtMem = mmap(0, vmsize, prot, flags, -1, 0);
    if ((uint64_t)(intptr_t)virtMem != 0xffffffffffffffff) {
      printf("%lx success (%p)\n", vmsize, virtMem);
      ((char*)virtMem)[0] = 'a';
      munmap(virtMem, vmsize);
      ok = mid;
    } else {
      printf("%lx failed (%p)\n", vmsize, virtMem);
      ng = mid;
    }
  }
  printf("finally %lfTiB\n", (double) ok / (1024llu * 1024 * 1024 * 1024));
  char* mem = (char*)mmap(0, ok, prot, flags, -1, 0);
  const uint64_t kPageSize = 4096;
  for (int64_t i = 0; i < ok; i += kPageSize) {
    mem[i] = 'a';
    printf("used %lf MiB\n", (double)i / (1024 * 1024));
    madvise(&mem[i], kPageSize, MADV_DONTNEED);
  }
}