Limiting the maximum size of a resource to optimize
Restricting and Controlling PageSpeed optimization rewriting
A resource with large content takes a long time and a large amount of memory to process. You can specify the maximum length (in bytes) of the content for PageSpeed to optimize. The default setting is -1, which means content of all lengths will be optimized.
pagespeed MaxCacheableContentLength -1
This directive can be used at the server level.