Function mi_large_huge_page_alloc

3rd/mimalloc-2.0.9/src/page.c:816–853

Large and huge page allocation. Huge pages are allocated directly without being in a queue. Because huge pages contain just one block, and the segment contains just that page, we always treat them as abandoned and any thread that frees the block can free the whole page and segment directly. Huge pages are also use if the requested alignment is very large (> MI_ALIGNMENT_MAX).

// that frees the block can free the whole page and segment directly.
// Huge pages are also use if the requested alignment is very large (> MI_ALIGNMENT_MAX).
static mi_page_t* mi_large_huge_page_alloc(mi_heap_t* heap, size_t size, size_t page_alignment) {
  size_t block_size = _mi_os_good_alloc_size(size);
  mi_assert_internal(mi_bin(block_size) == MI_BIN_HUGE || page_alignment > 0);
  bool is_huge = (block_size > MI_LARGE_OBJ_SIZE_MAX || page_alignment > 0);
  #if MI_HUGE_PAGE_ABANDON
  mi_page_queue_t* pq = (is_huge ? NULL : mi_page_queue(heap, block_size));
  #else
  mi_page_queue_t* pq = mi_page_queue(heap, is_huge ? MI_HUGE_BLOCK_SIZE : block_size); // not block_size as that can be low if the page_alignment > 0
  mi_assert_internal(!is_huge || mi_page_queue_is_huge(pq));
  #endif
  mi_page_t* page = mi_page_fresh_alloc(heap, pq, block_size, page_alignment);
  if (page != NULL) {
    mi_assert_internal(mi_page_immediate_available(page));
    
    if (is_huge) {
      mi_assert_internal(_mi_page_segment(page)->kind == MI_SEGMENT_HUGE);
      mi_assert_internal(_mi_page_segment(page)->used==1);
      #if MI_HUGE_PAGE_ABANDON
      mi_assert_internal(_mi_page_segment(page)->thread_id==0); // abandoned, not in the huge queue
      mi_page_set_heap(page, NULL);
      #endif      
    }
    else {
      mi_assert_internal(_mi_page_segment(page)->kind != MI_SEGMENT_HUGE);
    }
    
    const size_t bsize = mi_page_usable_block_size(page);  // note: not `mi_page_block_size` to account for padding
    if (bsize <= MI_LARGE_OBJ_SIZE_MAX) {
      mi_heap_stat_increase(heap, large, bsize);
      mi_heap_stat_counter_increase(heap, large_count, 1);
    }
    else {
      mi_heap_stat_increase(heap, huge, bsize);
      mi_heap_stat_counter_increase(heap, huge_count, 1);
    }
  }
  return page;
}


// Allocate a page