malloc callstack perf: lazy module lookups

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on December 01, 2010 09:48:55_

/\* XXX: when the app has a ton of mallocs that are quickly freed,
\* we spend a lot of time building and tearing down callstacks
\* (xref my original setup of not showing leak callstacks by default
\* which was for this reason and to save space: but for usability
\* it's better to have leak callstacks by default).
\* We could just record addresses and not modules, and only on
\* module unload or app exit walk the malloc table and fill
\* in the module info (and if too many unloads, switch to the
\* every-alloc scheme).
*/

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=75_