Function mi_region_try_alloc

3rd/mimalloc-2.0.9/src/region.c:265–340

static void* mi_region_try_alloc(size_t blocks, bool* commit, bool* large, bool* is_pinned, bool* is_zero, size_t* memid, mi_os_tld_t* tld)
{
  mi_assert_internal(blocks <= MI_BITMAP_FIELD_BITS);
  mem_region_t* region;
  mi_bitmap_index_t bit_idx;
  const int numa_node = (_mi_os_numa_node_count() <= 1 ? -1 : _mi_os_numa_node(tld));
  // try to claim in existing regions
  if (!mi_region_try_claim(numa_node, blocks, *large, &region, &bit_idx, tld)) {
    // otherwise try to allocate a fresh region and claim in there
    if (!mi_region_try_alloc_os(blocks, *commit, *large, &region, &bit_idx, tld)) {
      // out of regions or memory
      return NULL;
    }
  }

  // ------------------------------------------------
  // found a region and claimed `blocks` at `bit_idx`, initialize them now
  mi_assert_internal(region != NULL);
  mi_assert_internal(_mi_bitmap_is_claimed(&region->in_use, 1, blocks, bit_idx));

  mi_region_info_t info;
  info.value = mi_atomic_load_acquire(&region->info);
  uint8_t* start = (uint8_t*)mi_atomic_load_ptr_acquire(uint8_t,&region->start);
  mi_assert_internal(!(info.x.is_large && !*large));
  mi_assert_internal(start != NULL);

  *is_zero   = _mi_bitmap_claim(&region->dirty, 1, blocks, bit_idx, NULL);
  *large     = info.x.is_large;
  *is_pinned = info.x.is_pinned;
  *memid     = mi_memid_create(region, bit_idx);
  void* p = start + (mi_bitmap_index_bit_in_field(bit_idx) * MI_SEGMENT_SIZE);

  // commit
  if (*commit) {
    // ensure commit
    bool any_uncommitted;
    _mi_bitmap_claim(&region->commit, 1, blocks, bit_idx, &any_uncommitted);
    if (any_uncommitted) {
      mi_assert_internal(!info.x.is_large && !info.x.is_pinned);
      bool commit_zero = false;
      if (!_mi_mem_commit(p, blocks * MI_SEGMENT_SIZE, &commit_zero, tld)) {
        // failed to commit! unclaim and return
        mi_bitmap_unclaim(&region->in_use, 1, blocks, bit_idx);
        return NULL;
      }
      if (commit_zero) *is_zero = true;
    }
  }
  else {
    // no need to commit, but check if already fully committed
    *commit = _mi_bitmap_is_claimed(&region->commit, 1, blocks, bit_idx);
  }
  mi_assert_internal(!*commit || _mi_bitmap_is_claimed(&region->commit, 1, blocks, bit_idx));

  // unreset reset blocks
  if (_mi_bitmap_is_any_claimed(&region->reset, 1, blocks, bit_idx)) {
    // some blocks are still reset
    mi_assert_internal(!info.x.is_large && !info.x.is_pinned);