Function mi_segment_huge_page_alloc

3rd/mimalloc-2.0.9/src/segment.c:1521–1549

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static mi_page_t* mi_segment_huge_page_alloc(size_t size, size_t page_alignment, mi_arena_id_t req_arena_id, mi_segments_tld_t* tld, mi_os_tld_t* os_tld)
{
  mi_page_t* page = NULL;
  mi_segment_t* segment = mi_segment_alloc(size,page_alignment,req_arena_id,tld,os_tld,&page);
  if (segment == NULL || page==NULL) return NULL;
  mi_assert_internal(segment->used==1);
  mi_assert_internal(mi_page_block_size(page) >= size);  
  #if MI_HUGE_PAGE_ABANDON
  segment->thread_id = 0; // huge segments are immediately abandoned
  #endif  

  // for huge pages we initialize the xblock_size as we may
  // overallocate to accommodate large alignments.
  size_t psize;
  uint8_t* start = _mi_segment_page_start(segment, page, &psize);
  page->xblock_size = (psize > MI_HUGE_BLOCK_SIZE ? MI_HUGE_BLOCK_SIZE : (uint32_t)psize);
  
  // decommit the part of the prefix of a page that will not be used; this can be quite large (close to MI_SEGMENT_SIZE)
  if (page_alignment > 0 && segment->allow_decommit) {
    uint8_t* aligned_p = (uint8_t*)_mi_align_up((uintptr_t)start, page_alignment);
    mi_assert_internal(_mi_is_aligned(aligned_p, page_alignment));
    mi_assert_internal(psize - (aligned_p - start) >= size);      
    uint8_t* decommit_start = start + sizeof(mi_block_t);              // for the free list
    ptrdiff_t decommit_size = aligned_p - decommit_start;
    _mi_os_decommit(decommit_start, decommit_size, &_mi_stats_main);   // note: cannot use segment_decommit on huge segments    
  }
  
  return page;
}

#if MI_HUGE_PAGE_ABANDON
// free huge block from another thread