This release includes a few notable improvements, which are summarized below: 1) improved fast-path performance from the optimizations by @djwatson; 2) reduced virtual memory fragmentation and metadata usage; and 3) bug fixes on setting the number of background threads. In addition, peak / spike memory usage is improved with certain allocation patterns. As usual, the release and prior dev versions have gone through large-scale production testing.

New features:

• Implement oversize_threshold, which uses a dedicated arena for allocations crossing the specified threshold to reduce fragmentation. (@interwq)
• Add extents usage information to stats. (@tyleretzel)
• Log time information for sampled allocations. (@tyleretzel)
• Support 0 size in sdallocx. (@djwatson)
• Output rate for certain counters in malloc_stats. (@zinoale)
• Add configure option --enable-readlinkat, which allows the use of readlinkat over readlink. (@davidtgoldblatt)
• Add configure options --{enable,disable}-{static,shared} to allow not building unwanted libraries. (@Ericson2314)
• Add configure option --disable-libdl to enable fully static builds. (@interwq)
• Add mallctl interfaces:
  • opt.oversize_threshold (@interwq)
  • stats.arenas.<i>.extent_avail (@tyleretzel)
  • stats.arenas.<i>.extents.<j>.n{dirty,muzzy,retained} (@tyleretzel)
  • stats.arenas.<i>.extents.<j>.{dirty,muzzy,retained}_bytes (@tyleretzel)

Portability improvements:

• Update MSVC builds. (@maksqwe, @rustyx)
• Workaround a compiler optimizer bug on s390x. (@rkmisra)
• Make use of pthread_set_name_np(3) on FreeBSD. (@trasz)
• Implement malloc_getcpu() to enable percpu_arena for windows. (@santagada)
• Link against -pthread instead of -lpthread. (@paravoid)
• Make background_thread not dependent on libdl. (@interwq)
• Add stringify to fix a linker directive issue on MSVC. (@daverigby)
• Detect and fall back when 8-bit atomics are unavailable. (@interwq)
• Fall back to the default pthread_create(3) if dlsym(3) fails. (@interwq)

Optimizations and refactors:

• Refactor the TSD module. (@davidtgoldblatt)
• Avoid taking extents_muzzy mutex when muzzy is disabled. (@interwq)
• Avoid taking large_mtx for auto arenas on the tcache flush path. (@interwq)
• Optimize ixalloc by avoiding a size lookup. (@interwq)
• Implement opt.oversize_threshold which uses a dedicated arena for requests crossing the threshold, also eagerly purges the oversize extents. Default the threshold to 8 MiB. (@interwq)
• Clean compilation with -Wextra. (@gnzlbg, @jasone)
• Refactor the size class module. (@davidtgoldblatt)
• Refactor the stats emitter. (@tyleretzel)
• Optimize pow2_ceil. (@rkmisra)
• Avoid runtime detection of lazy purging on FreeBSD. (@trasz)
• Optimize mmap(2) alignment handling on FreeBSD. (@trasz)
• Improve error handling for THP state initialization. (@jsteemann)
• Rework the malloc() fast path. (@djwatson)
• Rework the free() fast path. (@djwatson)
• Refactor and optimize the tcache fill / flush paths. (@djwatson)
• Optimize sync / lwsync on PowerPC. (@chmeeedalf)
• Bypass extent_dalloc() when retain is enabled. (@interwq)
• Optimize the locking on large deallocation. (@interwq)
• Reduce the number of pages committed from sanity checking in debug build. (@trasz, @interwq)
• Deprecate OSSpinLock. (@interwq)
• Lower the default number of background threads to 4 (when the feature is enabled). (@interwq)
• Optimize the trylock spin wait. (@djwatson)
• Use arena index for arena-matching checks. (@interwq)
• Avoid forced decay on thread termination when using background threads. (@interwq)
• Disable muzzy decay by default. (@djwatson, @interwq)
• Only initialize libgcc unwinder when profiling is enabled. (@paravoid, @interwq)

Bug fixes (all only relevant to jemalloc 5.x):

• Fix background thread index issues with max_background_threads. (@djwatson, @interwq)
• Fix stats output for opt.lg_extent_max_active_fit. (@interwq)
• Fix opt.prof_prefix initialization. (@davidtgoldblatt)
• Properly trigger decay on tcache destroy. (@interwq, @amosbird)
• Fix tcache.flush. (@interwq)
• Detect whether explicit extent zero out is necessary with huge pages or custom extent hooks, which may change the purge semantics. (@interwq)
• Fix a side effect caused by extent_max_active_fit combined with decay-based purging, where freed extents can accumulate and not be reused for an extended period of time. (@interwq, @mpghf)
• Fix a missing unlock on extent register error handling. (@zoulasc)

Testing:

• Simplify the Travis script output. (@gnzlbg)
• Update the test scripts for FreeBSD. (@devnexen)
• Add unit tests for the producer-consumer pattern. (@interwq)
• Add Cirrus-CI config for FreeBSD builds. (@jasone)
• Add size-matching sanity checks on tcache flush. (@davidtgoldblatt, @interwq)

Incompatible changes:

• Remove --with-lg-page-sizes. (@davidtgoldblatt)

Documentation:

• Attempt to build docs by default, however skip doc building when xsltproc is missing. (@interwq, @cmuellner)