Improve Structure / Cache efficiency

Background: there is a new (experimental) valgrind tool called 'DHAT, a dynamic heap analysis tool'. It generates output a little like this. The data is rather hard to interpret, and has some false positives (eg. the opendir hits), but can point to large chunks of memory that are allocated written to, but then never read from, or identify holes in frequently used structures, and so on. It would be great to do further analysis on the data, discuss it on the list, and then patch the various classes / structures / calls in most need.

Skills: building, C++ hacking, C++ ABI understanding, patience.