I\'m using PHPStorm
under Win7 64bit
with 64bit Java (latest version I guess)
and working currently on an insanely big and chaotic project
I found a log file in the application which grew from a few KB to over 2 GB during a few seconds due to a bug. Webstorm was trying to index this 2 GB log file and running out of memory. Deleting the log file solved the problem (and then fixing the bug prevented the log file from growing).
Prior to this I also tried running the x64 JDK and increasing XMX to 2048. But in the end a 64 bit environment with 2048 MB wasn't enough (even though 512 MB was always enough before).