Function mi_page_extend_free

3rd/mimalloc-2.0.9/src/page.c:598–646

Extend the capacity (up to reserved) by initializing a free list We do at most `MI_MAX_EXTEND` to avoid touching too much memory Note: we also experimented with "bump" allocation on the first allocations but this did not speed up any benchmark (due to an extra test in malloc? or cache effects?)

// allocations but this did not speed up any benchmark (due to an
// extra test in malloc? or cache effects?)
static void mi_page_extend_free(mi_heap_t* heap, mi_page_t* page, mi_tld_t* tld) {
  MI_UNUSED(tld); 
  mi_assert_expensive(mi_page_is_valid_init(page));
  #if (MI_SECURE<=2)
  mi_assert(page->free == NULL);
  mi_assert(page->local_free == NULL);
  if (page->free != NULL) return;
  #endif
  if (page->capacity >= page->reserved) return;

  size_t page_size;
  _mi_page_start(_mi_page_segment(page), page, &page_size);
  mi_stat_counter_increase(tld->stats.pages_extended, 1);

  // calculate the extend count
  const size_t bsize = (page->xblock_size < MI_HUGE_BLOCK_SIZE ? page->xblock_size : page_size);
  size_t extend = page->reserved - page->capacity;
  mi_assert_internal(extend > 0);

  size_t max_extend = (bsize >= MI_MAX_EXTEND_SIZE ? MI_MIN_EXTEND : MI_MAX_EXTEND_SIZE/(uint32_t)bsize);
  if (max_extend < MI_MIN_EXTEND) { max_extend = MI_MIN_EXTEND; }
  mi_assert_internal(max_extend > 0);

  if (extend > max_extend) {
    // ensure we don't touch memory beyond the page to reduce page commit.
    // the `lean` benchmark tests this. Going from 1 to 8 increases rss by 50%.
    extend = max_extend;
  }

  mi_assert_internal(extend > 0 && extend + page->capacity <= page->reserved);
  mi_assert_internal(extend < (1UL<<16));

  // and append the extend the free list
  if (extend < MI_MIN_SLICES || MI_SECURE==0) { //!mi_option_is_enabled(mi_option_secure)) {
    mi_page_free_list_extend(page, bsize, extend, &tld->stats );
  }
  else {
    mi_page_free_list_extend_secure(heap, page, bsize, extend, &tld->stats);
  }
  // enable the new free list
  page->capacity += (uint16_t)extend;
  mi_stat_increase(tld->stats.page_committed, extend * bsize);

  // extension into zero initialized memory preserves the zero'd free list
  if (!page->is_zero_init) {
    page->is_zero = false;
  }
  mi_assert_expensive(mi_page_is_valid_init(page));
}

// Initialize a fresh page
static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi_tld_t* tld) {