title: Will MongoDB clean memory mapped files immediately after data resouce is moved to new shards?
body: <p>I am a newman for MongoDB and have a question about sharding.</p>
  
  <p>I've got to known that when a new shard is added into cluster. Balancer will move part of chunks from existing shards into the new one.</p>
  
  <p>But since MongoDB uses memory mapped file to map the data source into memory, my question is: will memory mapped file will also be "remapped" immediately after chunks on disk has been moved?</p>
  
  <p>For example, currently I have shard 1 and shard 2, each shard is running in one machine, then a new machine is added as shard 3. For the machine storing shard 2, some chunks  are moved out to shard 3, but in its memory, is it true that those memory mapped files which mapps the removed data will also be cleaned immediately?</p>