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https://github.com/jemalloc/jemalloc
+* 4.2.0 (XXX)
+
+ 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:
+ - Link against librt for clock_gettime(2) if glibc < 2.17. (@jasone)
+ - Scale leak report summary according to sampling probability. (@jasone)
+
* 4.1.1 (May 3, 2016)
This bugfix release resolves a variety of mostly minor issues, though the