Function _mi_mem_free

3rd/mimalloc-2.0.9/src/region.c:393–447

Free previously allocated memory with a given id.

// Free previously allocated memory with a given id.
void _mi_mem_free(void* p, size_t size, size_t alignment, size_t align_offset, size_t id, bool full_commit, bool any_reset, mi_os_tld_t* tld) {
  mi_assert_internal(size > 0 && tld != NULL);
  if (p==NULL) return;
  if (size==0) return;
  size = _mi_align_up(size, _mi_os_page_size());

  size_t arena_memid = 0;
  mi_bitmap_index_t bit_idx;
  mem_region_t* region;
  if (mi_memid_is_arena(id,&region,&bit_idx,&arena_memid)) {
   // was a direct arena allocation, pass through
    _mi_arena_free(p, size, alignment, align_offset, arena_memid, full_commit, tld->stats);
  }
  else {
    // allocated in a region
    mi_assert_internal(align_offset == 0);
    mi_assert_internal(size <= MI_REGION_MAX_OBJ_SIZE); if (size > MI_REGION_MAX_OBJ_SIZE) return;
    const size_t blocks = mi_region_block_count(size);
    mi_assert_internal(blocks + bit_idx <= MI_BITMAP_FIELD_BITS);
    mi_region_info_t info;
    info.value = mi_atomic_load_acquire(&region->info);
    mi_assert_internal(info.value != 0);
    void* blocks_start = mi_region_blocks_start(region, bit_idx);
    mi_assert_internal(blocks_start == p); // not a pointer in our area?
    mi_assert_internal(bit_idx + blocks <= MI_BITMAP_FIELD_BITS);
    if (blocks_start != p || bit_idx + blocks > MI_BITMAP_FIELD_BITS) return; // or `abort`?

    // committed?
    if (full_commit && (size % MI_SEGMENT_SIZE) == 0) {
      _mi_bitmap_claim(&region->commit, 1, blocks, bit_idx, NULL);
    }

    if (any_reset) {
      // set the is_reset bits if any pages were reset
      _mi_bitmap_claim(&region->reset, 1, blocks, bit_idx, NULL);
    }

    // reset the blocks to reduce the working set.
    if (!info.x.is_large && !info.x.is_pinned && mi_option_is_enabled(mi_option_segment_reset)
       && (mi_option_is_enabled(mi_option_eager_commit) ||
           mi_option_is_enabled(mi_option_reset_decommits))) // cannot reset halfway committed segments, use only `option_page_reset` instead
    {
      bool any_unreset;
      _mi_bitmap_claim(&region->reset, 1, blocks, bit_idx, &any_unreset);
      if (any_unreset) {
        _mi_abandoned_await_readers(); // ensure no more pending write (in case reset = decommit)
        _mi_mem_reset(p, blocks * MI_SEGMENT_SIZE, tld);
      }
    }

    // and unclaim
    bool all_unclaimed = mi_bitmap_unclaim(&region->in_use, 1, blocks, bit_idx);
    mi_assert_internal(all_unclaimed); MI_UNUSED(all_unclaimed);
  }
}


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