title: Keras clear all gpu memory
body: <p>I'm doing something like this:</p>
  
  <pre><code>for ai in ai_generator:
     ai.fit(ecc...)
  </code></pre>
  
  <p>ai_generator is a generator that instantiate a model with different configuration.<br/>
  My problem is gpu memory overflow, and K.clear_session() don't work because it throw this<br/> <code>ValueError: Tensor("conv2d_1/kernel:0", shape=(3, 3, 1, 1), dtype=float32_ref) must be from the same graph as Tensor("concat:0", shape=(?, 38, 300, 1), dtype=float32).</code><br/>
  How can I clear keras memory as new?
  I need only performances of fit method, I can delete all.</p>