For a long time been trying to figure out Safari hogging so much RAM & VM.
Most things I've read attribute it to Extensions & Add-ons, & that certainly is a big part of the problem, as it seems to multiply them for every tab & window, I disabled wall of them & saved a few 100K, but it would eventually creep up leaving zero free RAM of my precious 6 GB.
Finally took a look at ~/Library/Preferences/com/safari/plist
Holy cow it had entries for I think every site I ever visited.. hundreds of entries like this…
So, I renamed that & let Safari build a new one, on next launch & running days with the same tabs & windows open I was saving 1 GB of Real Memory in Web Processes & a couple 100 K in Safari, didn't keep track of VM, but assume it was less also.
It appears that Safari Web Processes uses all those entries whether you're on those sites or not!???
This is on Mid 2007 iMac, OSX 10.8.5, Safari 6.2.8 (8522.214.171.124.1)