Method trim

thread/stack-allocator.cpp:128–140

        return 0;
    }
    size_t trim(size_t keep_size) {
        size_t count = 0;
        for (int i = 0; in_pool_size > keep_size; i = (i + 1) % N_SLOTS) {
            if (!slots[i].pool.empty()) {
                auto ptr = slots[i].pool.back();
                slots[i].pool.pop_back();
                in_pool_size -= slots[i].slotsize;
                count += slots[i].slotsize;
                __dealloc(ptr, slots[i].slotsize);
            }
        }
        return count;
    }
    size_t threshold(size_t x) {
        trim_threshold = x;
        return trim_threshold;