Function mi_page_queue_find_free_ex

3rd/mimalloc-2.0.9/src/page.c:703–752

Find a page with free blocks of `page->block_size`.

// Find a page with free blocks of `page->block_size`.
static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* pq, bool first_try)
{
  // search through the pages in "next fit" order
  size_t count = 0;
  mi_page_t* page = pq->first;
  while (page != NULL)
  {
    mi_page_t* next = page->next; // remember next
    count++;

    // 0. collect freed blocks by us and other threads
    _mi_page_free_collect(page, false);

    // 1. if the page contains free blocks, we are done
    if (mi_page_immediate_available(page)) {
      break;  // pick this one
    }

    // 2. Try to extend
    if (page->capacity < page->reserved) {
      mi_page_extend_free(heap, page, heap->tld);
      mi_assert_internal(mi_page_immediate_available(page));
      break;
    }

    // 3. If the page is completely full, move it to the `mi_pages_full`
    // queue so we don't visit long-lived pages too often.
    mi_assert_internal(!mi_page_is_in_full(page) && !mi_page_immediate_available(page));
    mi_page_to_full(page, pq);

    page = next;
  } // for each page

  mi_heap_stat_counter_increase(heap, searches, count);

  if (page == NULL) {
    _mi_heap_collect_retired(heap, false); // perhaps make a page available?
    page = mi_page_fresh(heap, pq);
    if (page == NULL && first_try) {
      // out-of-memory _or_ an abandoned page with free blocks was reclaimed, try once again
      page = mi_page_queue_find_free_ex(heap, pq, false);
    }
  }
  else {
    mi_assert(pq->first == page);
    page->retire_expire = 0;
  }
  mi_assert_internal(page == NULL || mi_page_immediate_available(page));
  return page;
}