See here: http://deeplearning.net/software/theano/library/config.html
You can change this in the environment variables. I added the following to my .theanorc file and saw significant speed increases during training of a cnn:
[lib] cnmem=.75
Beyond .75 I got out of memory errors, but I‘d imagine this varies based on your setup.
原文：http://www.cnblogs.com/anyview/p/5441925.html