Function mi_segment_try_reclaim

3rd/mimalloc-2.0.9/src/segment.c:1396–1432

}

static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slices, size_t block_size, bool* reclaimed, mi_segments_tld_t* tld)
{
  *reclaimed = false;
  mi_segment_t* segment;
  long max_tries = mi_option_get_clamp(mi_option_max_segment_reclaim, 8, 1024);     // limit the work to bound allocation times
  while ((max_tries-- > 0) && ((segment = mi_abandoned_pop()) != NULL)) {
    segment->abandoned_visits++;
    // todo: an arena exclusive heap will potentially visit many abandoned unsuitable segments
    // and push them into the visited list and use many tries. Perhaps we can skip non-suitable ones in a better way?
    bool is_suitable = _mi_heap_memid_is_suitable(heap, segment->memid);
    bool has_page = mi_segment_check_free(segment,needed_slices,block_size,tld); // try to free up pages (due to concurrent frees)
    if (segment->used == 0) {
      // free the segment (by forced reclaim) to make it available to other threads.
      // note1: we prefer to free a segment as that might lead to reclaiming another
      // segment that is still partially used.
      // note2: we could in principle optimize this by skipping reclaim and directly
      // freeing but that would violate some invariants temporarily)
      mi_segment_reclaim(segment, heap, 0, NULL, tld);
    }
    else if (has_page && is_suitable) {
      // found a large enough free span, or a page of the right block_size with free space 
      // we return the result of reclaim (which is usually `segment`) as it might free
      // the segment due to concurrent frees (in which case `NULL` is returned).
      return mi_segment_reclaim(segment, heap, block_size, reclaimed, tld);
    }
    else if (segment->abandoned_visits > 3 && is_suitable) {  
      // always reclaim on 3rd visit to limit the abandoned queue length.
      mi_segment_reclaim(segment, heap, 0, NULL, tld);
    }
    else {
      // otherwise, push on the visited list so it gets not looked at too quickly again
      mi_segment_delayed_decommit(segment, true /* force? */, tld->stats); // forced decommit if needed as we may not visit soon again
      mi_abandoned_visited_push(segment);
    }
  }
  return NULL;
}


void _mi_abandoned_collect(mi_heap_t* heap, bool force, mi_segments_tld_t* tld)