Method Scavenge

libs/tcmalloc-1.4/src/thread_cache.cc:235–271

Release idle memory to the central cache

// Release idle memory to the central cache
void ThreadCache::Scavenge() {
  // If the low-water mark for the free list is L, it means we would
  // not have had to allocate anything from the central cache even if
  // we had reduced the free list size by L.  We aim to get closer to
  // that situation by dropping L/2 nodes from the free list.  This
  // may not release much memory, but if so we will call scavenge again
  // pretty soon and the low-water marks will be high on that call.
  //int64 start = CycleClock::Now();
  for (unsigned int cl = 0; cl < kNumClasses; cl++) {
    FreeList* list = &list_[cl];
    const int lowmark = list->lowwatermark();
    if (lowmark > 0) {
      const int drop = (lowmark > 1) ? lowmark/2 : 1;
      ReleaseToCentralCache(list, cl, drop);

      // Shrink the max length if it isn't used.  Only shrink down to
      // batch_size -- if the thread was active enough to get the max_length
      // above batch_size, it will likely be that active again.  If
      // max_length shinks below batch_size, the thread will have to
      // go through the slow-start behavior again.  The slow-start is useful
      // mainly for threads that stay relatively idle for their entire
      // lifetime.
      const int batch_size = Static::sizemap()->num_objects_to_move(cl);
      if (static_cast<int>(list->max_length()) > batch_size) {
        list->set_max_length(
            max<int>(list->max_length() - batch_size, batch_size));
      }
    }
    list->clear_lowwatermark();
  }

  IncreaseCacheLimit();

//   int64 finish = CycleClock::Now();
//   CycleTimer ct;
//   MESSAGE("GC: %.0f ns\n", ct.CyclesToUsec(finish-start)*1000.0);
}

void ThreadCache::IncreaseCacheLimit() {
  SpinLockHolder h(Static::pageheap_lock());