Thank you, @smth.
You must have meant to say “allocate 350MB” 
Having 1.7GB available (free+cached) and not being able to use even 20% of it. Ouch!
Is there some function I can call to defrag it? I don’t care if it takes time to do so.
What causes such fragmentation and how can it be avoided? Perhaps this is documented already?
Thank you.