New features:

• Add the arena.<i>.reset mallctl, which makes it possible to discard all of an arena's allocations in a single operation. (@jasone)
• Add the stats.retained and stats.arenas.<i>.retained statistics. (@jasone)
• Add the --with-version configure option. (@jasone)
• Support --with-lg-page values larger than actual page size. (@jasone)

Optimizations:

• Use pairing heaps rather than red-black trees for various hot data structures. (@djwatson, @jasone)
• Streamline fast paths of rtree operations. (@jasone)
• Optimize the fast paths of calloc() and [m,d,sd]allocx(). (@jasone)
• Decommit unused virtual memory if the OS does not overcommit. (@jasone)
• Specify MAP_NORESERVE on Linux if [heuristic] overcommit is active, in order to avoid unfortunate interactions during fork(2). (@jasone)

Bug fixes:

• Fix chunk accounting related to triggering gdump profiles. (@jasone)
• Link against librt for clock_gettime(2) if glibc < 2.17. (@jasone)
• Scale leak report summary according to sampling probability. (@jasone)