jemalloc 4.2.0 released

[Jason Evans]

jemalloc 4.2.0 is now available.

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)

For the complete ChangeLog, see:
	https://github.com/jemalloc/jemalloc/raw/4.2.0/ChangeLog

Direct download:
	https://github.com/jemalloc/jemalloc/releases/download/4.2.0/jemalloc-4.2.0.tar.bz2

Starting point for general information:
	http://www.canonware.com/jemalloc/

Browsable revision history:
	https://github.com/jemalloc/jemalloc/tree/4.2.0