noatimeoption in fstab for the partition. So, access times for files were being updated in real time. I do not need that at all. Access times are updated even for page cache hits, which is of no use to me. So, I turned it off by changing the mount options for the partition.
bin/rubymine64.vmoptionsand edit it to reflect the following.
ReservedCodeCacheSize. It was also having the same value as the 32-bit version, i.e. 64mb. Changing it as follows, improved performance.