Gpu memory pool code confusing

[ximitiejiang]

hello, i am learning the code of gpu memory pool and felt confusing for below code:

ppl.cv/src/ppl/cv/cuda/utility/memory_pool.cpp

Line 105 in 6f65a8d

while (current != memory_blocks_.end()) {

my understanding is: this while loop is to make previous iterator point to the last block and current iterator point to end of block container then we can create a new block after the last block and insert to end of block container.
but why we need below "if"?
i think this would lead to create a new block between previous and current block, seems not make sense....

    hollow_begin = previous->data + previous->size;
    if (hollow_begin + allocated_size <= current->data) {
      memory_block.data = hollow_begin;
      memory_block.pitch = 0;
      memory_block.size = allocated_size;

      host_mutex_.lock();
      memory_blocks_.insert_after(previous, memory_block);
      host_mutex_.unlock();

      return;
    } 

maybe i missed some logic, please correct me, thank you in advance.