Comment 4 for bug 1208993

I am affected by this problem too, running Ubuntu 14.04 64 bit.

"dirty files" seem to cause this problem on 64 bit systems. I solved it on my system by decreasing the dirty files cache. This article explains it in detail: http://lonesysadmin.net/2013/12/22/better-linux-disk-caching-performance-vm-dirty_ratio/