xref: /freebsd/contrib/jemalloc/ChangeLog (revision b7eaed250fccfdef218a62bc2d0af529ad75341c)

Following are change highlights associated with official releases.  Important
bug fixes are all mentioned, but some internal enhancements are omitted here for
brevity.  Much more detail can be found in the git revision history:

    https://github.com/jemalloc/jemalloc

* 5.0.0 (June 13, 2017)

  Unlike all previous jemalloc releases, this release does not use naturally
  aligned "chunks" for virtual memory management, and instead uses page-aligned
  "extents".  This change has few externally visible effects, but the internal
  impacts are... extensive.  Many other internal changes combine to make this
  the most cohesively designed version of jemalloc so far, with ample
  opportunity for further enhancements.

  Continuous integration is now an integral aspect of development thanks to the
  efforts of @davidtgoldblatt, and the dev branch tends to remain reasonably
  stable on the tested platforms (Linux, FreeBSD, macOS, and Windows).  As a
  side effect the official release frequency may decrease over time.

  New features:
  - Implement optional per-CPU arena support; threads choose which arena to use
    based on current CPU rather than on fixed thread-->arena associations.
    (@interwq)
  - Implement two-phase decay of unused dirty pages.  Pages transition from
    dirty-->muzzy-->clean, where the first phase transition relies on
    madvise(... MADV_FREE) semantics, and the second phase transition discards
    pages such that they are replaced with demand-zeroed pages on next access.
    (@jasone)
  - Increase decay time resolution from seconds to milliseconds.  (@jasone)
  - Implement opt-in per CPU background threads, and use them for asynchronous
    decay-driven unused dirty page purging.  (@interwq)
  - Add mutex profiling, which collects a variety of statistics useful for
    diagnosing overhead/contention issues.  (@interwq)
  - Add C++ new/delete operator bindings.  (@djwatson)
  - Support manually created arena destruction, such that all data and metadata
    are discarded.  Add MALLCTL_ARENAS_DESTROYED for accessing merged stats
    associated with destroyed arenas.  (@jasone)
  - Add MALLCTL_ARENAS_ALL as a fixed index for use in accessing
    merged/destroyed arena statistics via mallctl.  (@jasone)
  - Add opt.abort_conf to optionally abort if invalid configuration options are
    detected during initialization.  (@interwq)
  - Add opt.stats_print_opts, so that e.g. JSON output can be selected for the
    stats dumped during exit if opt.stats_print is true.  (@jasone)
  - Add --with-version=VERSION for use when embedding jemalloc into another
    project's git repository.  (@jasone)
  - Add --disable-thp to support cross compiling.  (@jasone)
  - Add --with-lg-hugepage to support cross compiling.  (@jasone)
  - Add mallctl interfaces (various authors):
    + background_thread
    + opt.abort_conf
    + opt.retain
    + opt.percpu_arena
    + opt.background_thread
    + opt.{dirty,muzzy}_decay_ms
    + opt.stats_print_opts
    + arena.<i>.initialized
    + arena.<i>.destroy
    + arena.<i>.{dirty,muzzy}_decay_ms
    + arena.<i>.extent_hooks
    + arenas.{dirty,muzzy}_decay_ms
    + arenas.bin.<i>.slab_size
    + arenas.nlextents
    + arenas.lextent.<i>.size
    + arenas.create
    + stats.background_thread.{num_threads,num_runs,run_interval}
    + stats.mutexes.{ctl,background_thread,prof,reset}.
      {num_ops,num_spin_acq,num_wait,max_wait_time,total_wait_time,max_num_thds,
      num_owner_switch}
    + stats.arenas.<i>.{dirty,muzzy}_decay_ms
    + stats.arenas.<i>.uptime
    + stats.arenas.<i>.{pmuzzy,base,internal,resident}
    + stats.arenas.<i>.{dirty,muzzy}_{npurge,nmadvise,purged}
    + stats.arenas.<i>.bins.<j>.{nslabs,reslabs,curslabs}
    + stats.arenas.<i>.bins.<j>.mutex.
      {num_ops,num_spin_acq,num_wait,max_wait_time,total_wait_time,max_num_thds,
      num_owner_switch}
    + stats.arenas.<i>.lextents.<j>.{nmalloc,ndalloc,nrequests,curlextents}
    + stats.arenas.i.mutexes.{large,extent_avail,extents_dirty,extents_muzzy,
      extents_retained,decay_dirty,decay_muzzy,base,tcache_list}.
      {num_ops,num_spin_acq,num_wait,max_wait_time,total_wait_time,max_num_thds,
      num_owner_switch}

  Portability improvements:
  - Improve reentrant allocation support, such that deadlock is less likely if
    e.g. a system library call in turn allocates memory.  (@davidtgoldblatt,
    @interwq)
  - Support static linking of jemalloc with glibc.  (@djwatson)

  Optimizations and refactors:
  - Organize virtual memory as "extents" of virtual memory pages, rather than as
    naturally aligned "chunks", and store all metadata in arbitrarily distant
    locations.  This reduces virtual memory external fragmentation, and will
    interact better with huge pages (not yet explicitly supported).  (@jasone)
  - Fold large and huge size classes together; only small and large size classes
    remain.  (@jasone)
  - Unify the allocation paths, and merge most fast-path branching decisions.
    (@davidtgoldblatt, @interwq)
  - Embed per thread automatic tcache into thread-specific data, which reduces
    conditional branches and dereferences.  Also reorganize tcache to increase
    fast-path data locality.  (@interwq)
  - Rewrite atomics to closely model the C11 API, convert various
    synchronization from mutex-based to atomic, and use the explicit memory
    ordering control to resolve various hypothetical races without increasing
    synchronization overhead.  (@davidtgoldblatt)
  - Extensively optimize rtree via various methods:
    + Add multiple layers of rtree lookup caching, since rtree lookups are now
      part of fast-path deallocation.  (@interwq)
    + Determine rtree layout at compile time.  (@jasone)
    + Make the tree shallower for common configurations.  (@jasone)
    + Embed the root node in the top-level rtree data structure, thus avoiding
      one level of indirection.  (@jasone)
    + Further specialize leaf elements as compared to internal node elements,
      and directly embed extent metadata needed for fast-path deallocation.
      (@jasone)
    + Ignore leading always-zero address bits (architecture-specific).
      (@jasone)
  - Reorganize headers (ongoing work) to make them hermetic, and disentangle
    various module dependencies.  (@davidtgoldblatt)
  - Convert various internal data structures such as size class metadata from
    boot-time-initialized to compile-time-initialized.  Propagate resulting data
    structure simplifications, such as making arena metadata fixed-size.
    (@jasone)
  - Simplify size class lookups when constrained to size classes that are
    multiples of the page size.  This speeds lookups, but the primary benefit is
    complexity reduction in code that was the source of numerous regressions.
    (@jasone)
  - Lock individual extents when possible for localized extent operations,
    rather than relying on a top-level arena lock.  (@davidtgoldblatt, @jasone)
  - Use first fit layout policy instead of best fit, in order to improve
    packing.  (@jasone)
  - If munmap(2) is not in use, use an exponential series to grow each arena's
    virtual memory, so that the number of disjoint virtual memory mappings
    remains low.  (@jasone)
  - Implement per arena base allocators, so that arenas never share any virtual
    memory pages.  (@jasone)
  - Automatically generate private symbol name mangling macros.  (@jasone)

  Incompatible changes:
  - Replace chunk hooks with an expanded/normalized set of extent hooks.
    (@jasone)
  - Remove ratio-based purging.  (@jasone)
  - Remove --disable-tcache.  (@jasone)
  - Remove --disable-tls.  (@jasone)
  - Remove --enable-ivsalloc.  (@jasone)
  - Remove --with-lg-size-class-group.  (@jasone)
  - Remove --with-lg-tiny-min.  (@jasone)
  - Remove --disable-cc-silence.  (@jasone)
  - Remove --enable-code-coverage.  (@jasone)
  - Remove --disable-munmap (replaced by opt.retain).  (@jasone)
  - Remove Valgrind support.  (@jasone)
  - Remove quarantine support.  (@jasone)
  - Remove redzone support.  (@jasone)
  - Remove mallctl interfaces (various authors):
    + config.munmap
    + config.tcache
    + config.tls
    + config.valgrind
    + opt.lg_chunk
    + opt.purge
    + opt.lg_dirty_mult
    + opt.decay_time
    + opt.quarantine
    + opt.redzone
    + opt.thp
    + arena.<i>.lg_dirty_mult
    + arena.<i>.decay_time
    + arena.<i>.chunk_hooks
    + arenas.initialized
    + arenas.lg_dirty_mult
    + arenas.decay_time
    + arenas.bin.<i>.run_size
    + arenas.nlruns
    + arenas.lrun.<i>.size
    + arenas.nhchunks
    + arenas.hchunk.<i>.size
    + arenas.extend
    + stats.cactive
    + stats.arenas.<i>.lg_dirty_mult
    + stats.arenas.<i>.decay_time
    + stats.arenas.<i>.metadata.{mapped,allocated}
    + stats.arenas.<i>.{npurge,nmadvise,purged}
    + stats.arenas.<i>.huge.{allocated,nmalloc,ndalloc,nrequests}
    + stats.arenas.<i>.bins.<j>.{nruns,reruns,curruns}
    + stats.arenas.<i>.lruns.<j>.{nmalloc,ndalloc,nrequests,curruns}
    + stats.arenas.<i>.hchunks.<j>.{nmalloc,ndalloc,nrequests,curhchunks}

  Bug fixes:
  - Improve interval-based profile dump triggering to dump only one profile when
    a single allocation's size exceeds the interval.  (@jasone)
  - Use prefixed function names (as controlled by --with-jemalloc-prefix) when
    pruning backtrace frames in jeprof.  (@jasone)

* 4.5.0 (February 28, 2017)

  This is the first release to benefit from much broader continuous integration
  testing, thanks to @davidtgoldblatt.  Had we had this testing infrastructure
  in place for prior releases, it would have caught all of the most serious
  regressions fixed by this release.

  New features:
  - Add --disable-thp and the opt.thp mallctl to provide opt-out mechanisms for
    transparent huge page integration.  (@jasone)
  - Update zone allocator integration to work with macOS 10.12.  (@glandium)
  - Restructure *CFLAGS configuration, so that CFLAGS behaves typically, and
    EXTRA_CFLAGS provides a way to specify e.g. -Werror during building, but not
    during configuration.  (@jasone, @ronawho)

  Bug fixes:
  - Fix DSS (sbrk(2)-based) allocation.  This regression was first released in
    4.3.0.  (@jasone)
  - Handle race in per size class utilization computation.  This functionality
    was first released in 4.0.0.  (@interwq)
  - Fix lock order reversal during gdump.  (@jasone)
  - Fix/refactor tcache synchronization.  This regression was first released in
    4.0.0.  (@jasone)
  - Fix various JSON-formatted malloc_stats_print() bugs.  This functionality
    was first released in 4.3.0.  (@jasone)
  - Fix huge-aligned allocation.  This regression was first released in 4.4.0.
    (@jasone)
  - When transparent huge page integration is enabled, detect what state pages
    start in according to the kernel's current operating mode, and only convert
    arena chunks to non-huge during purging if that is not their initial state.
    This functionality was first released in 4.4.0.  (@jasone)
  - Fix lg_chunk clamping for the --enable-cache-oblivious --disable-fill case.
    This regression was first released in 4.0.0.  (@jasone, @428desmo)
  - Properly detect sparc64 when building for Linux.  (@glaubitz)

* 4.4.0 (December 3, 2016)

  New features:
  - Add configure support for *-*-linux-android.  (@cferris1000, @jasone)
  - Add the --disable-syscall configure option, for use on systems that place
    security-motivated limitations on syscall(2).  (@jasone)
  - Add support for Debian GNU/kFreeBSD.  (@thesam)

  Optimizations:
  - Add extent serial numbers and use them where appropriate as a sort key that
    is higher priority than address, so that the allocation policy prefers older
    extents.  This tends to improve locality (decrease fragmentation) when
    memory grows downward.  (@jasone)
  - Refactor madvise(2) configuration so that MADV_FREE is detected and utilized
    on Linux 4.5 and newer.  (@jasone)
  - Mark partially purged arena chunks as non-huge-page.  This improves
    interaction with Linux's transparent huge page functionality.  (@jasone)

  Bug fixes:
  - Fix size class computations for edge conditions involving extremely large
    allocations.  This regression was first released in 4.0.0.  (@jasone,
    @ingvarha)
  - Remove overly restrictive assertions related to the cactive statistic.  This
    regression was first released in 4.1.0.  (@jasone)
  - Implement a more reliable detection scheme for os_unfair_lock on macOS.
    (@jszakmeister)

* 4.3.1 (November 7, 2016)

  Bug fixes:
  - Fix a severe virtual memory leak.  This regression was first released in
    4.3.0.  (@interwq, @jasone)
  - Refactor atomic and prng APIs to restore support for 32-bit platforms that
    use pre-C11 toolchains, e.g. FreeBSD's mips.  (@jasone)

* 4.3.0 (November 4, 2016)

  This is the first release that passes the test suite for multiple Windows
  configurations, thanks in large part to @glandium setting up continuous
  integration via AppVeyor (and Travis CI for Linux and OS X).

  New features:
  - Add "J" (JSON) support to malloc_stats_print().  (@jasone)
  - Add Cray compiler support.  (@ronawho)

  Optimizations:
  - Add/use adaptive spinning for bootstrapping and radix tree node
    initialization.  (@jasone)

  Bug fixes:
  - Fix large allocation to search starting in the optimal size class heap,
    which can substantially reduce virtual memory churn and fragmentation.  This
    regression was first released in 4.0.0.  (@mjp41, @jasone)
  - Fix stats.arenas.<i>.nthreads accounting.  (@interwq)
  - Fix and simplify decay-based purging.  (@jasone)
  - Make DSS (sbrk(2)-related) operations lockless, which resolves potential
    deadlocks during thread exit.  (@jasone)
  - Fix over-sized allocation of radix tree leaf nodes.  (@mjp41, @ogaun,
    @jasone)
  - Fix over-sized allocation of arena_t (plus associated stats) data
    structures.  (@jasone, @interwq)
  - Fix EXTRA_CFLAGS to not affect configuration.  (@jasone)
  - Fix a Valgrind integration bug.  (@ronawho)
  - Disallow 0x5a junk filling when running in Valgrind.  (@jasone)
  - Fix a file descriptor leak on Linux.  This regression was first released in
    4.2.0.  (@vsarunas, @jasone)
  - Fix static linking of jemalloc with glibc.  (@djwatson)
  - Use syscall(2) rather than {open,read,close}(2) during boot on Linux.  This
    works around other libraries' system call wrappers performing reentrant
    allocation.  (@kspinka, @Whissi, @jasone)
  - Fix OS X default zone replacement to work with OS X 10.12.  (@glandium,
    @jasone)
  - Fix cached memory management to avoid needless commit/decommit operations
    during purging, which resolves permanent virtual memory map fragmentation
    issues on Windows.  (@mjp41, @jasone)
  - Fix TSD fetches to avoid (recursive) allocation.  This is relevant to
    non-TLS and Windows configurations.  (@jasone)
  - Fix malloc_conf overriding to work on Windows.  (@jasone)
  - Forcibly disable lazy-lock on Windows (was forcibly *enabled*).  (@jasone)

* 4.2.1 (June 8, 2016)

  Bug fixes:
  - Fix bootstrapping issues for configurations that require allocation during
    tsd initialization (e.g. --disable-tls).  (@cferris1000, @jasone)
  - Fix gettimeofday() version of nstime_update().  (@ronawho)
  - Fix Valgrind regressions in calloc() and chunk_alloc_wrapper().  (@ronawho)
  - Fix potential VM map fragmentation regression.  (@jasone)
  - Fix opt_zero-triggered in-place huge reallocation zeroing.  (@jasone)
  - Fix heap profiling context leaks in reallocation edge cases.  (@jasone)

* 4.2.0 (May 12, 2016)

  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)

* 4.1.1 (May 3, 2016)

  This bugfix release resolves a variety of mostly minor issues, though the
  bitmap fix is critical for 64-bit Windows.

  Bug fixes:
  - Fix the linear scan version of bitmap_sfu() to shift by the proper amount
    even when sizeof(long) is not the same as sizeof(void *), as on 64-bit
    Windows.  (@jasone)
  - Fix hashing functions to avoid unaligned memory accesses (and resulting
    crashes).  This is relevant at least to some ARM-based platforms.
    (@rkmisra)
  - Fix fork()-related lock rank ordering reversals.  These reversals were
    unlikely to cause deadlocks in practice except when heap profiling was
    enabled and active.  (@jasone)
  - Fix various chunk leaks in OOM code paths.  (@jasone)
  - Fix malloc_stats_print() to print opt.narenas correctly.  (@jasone)
  - Fix MSVC-specific build/test issues.  (@rustyx, @yuslepukhin)
  - Fix a variety of test failures that were due to test fragility rather than
    core bugs.  (@jasone)

* 4.1.0 (February 28, 2016)

  This release is primarily about optimizations, but it also incorporates a lot
  of portability-motivated refactoring and enhancements.  Many people worked on
  this release, to an extent that even with the omission here of minor changes
  (see git revision history), and of the people who reported and diagnosed
  issues, so much of the work was contributed that starting with this release,
  changes are annotated with author credits to help reflect the collaborative
  effort involved.

  New features:
  - Implement decay-based unused dirty page purging, a major optimization with
    mallctl API impact.  This is an alternative to the existing ratio-based
    unused dirty page purging, and is intended to eventually become the sole
    purging mechanism.  New mallctls:
    + opt.purge
    + opt.decay_time
    + arena.<i>.decay
    + arena.<i>.decay_time
    + arenas.decay_time
    + stats.arenas.<i>.decay_time
    (@jasone, @cevans87)
  - Add --with-malloc-conf, which makes it possible to embed a default
    options string during configuration.  This was motivated by the desire to
    specify --with-malloc-conf=purge:decay , since the default must remain
    purge:ratio until the 5.0.0 release.  (@jasone)
  - Add MS Visual Studio 2015 support.  (@rustyx, @yuslepukhin)
  - Make *allocx() size class overflow behavior defined.  The maximum
    size class is now less than PTRDIFF_MAX to protect applications against
    numerical overflow, and all allocation functions are guaranteed to indicate
    errors rather than potentially crashing if the request size exceeds the
    maximum size class.  (@jasone)
  - jeprof:
    + Add raw heap profile support.  (@jasone)
    + Add --retain and --exclude for backtrace symbol filtering.  (@jasone)

  Optimizations:
  - Optimize the fast path to combine various bootstrapping and configuration
    checks and execute more streamlined code in the common case.  (@interwq)
  - Use linear scan for small bitmaps (used for small object tracking).  In
    addition to speeding up bitmap operations on 64-bit systems, this reduces
    allocator metadata overhead by approximately 0.2%.  (@djwatson)
  - Separate arena_avail trees, which substantially speeds up run tree
    operations.  (@djwatson)
  - Use memoization (boot-time-computed table) for run quantization.  Separate
    arena_avail trees reduced the importance of this optimization.  (@jasone)
  - Attempt mmap-based in-place huge reallocation.  This can dramatically speed
    up incremental huge reallocation.  (@jasone)

  Incompatible changes:
  - Make opt.narenas unsigned rather than size_t.  (@jasone)

  Bug fixes:
  - Fix stats.cactive accounting regression.  (@rustyx, @jasone)
  - Handle unaligned keys in hash().  This caused problems for some ARM systems.
    (@jasone, @cferris1000)
  - Refactor arenas array.  In addition to fixing a fork-related deadlock, this
    makes arena lookups faster and simpler.  (@jasone)
  - Move retained memory allocation out of the default chunk allocation
    function, to a location that gets executed even if the application installs
    a custom chunk allocation function.  This resolves a virtual memory leak.
    (@buchgr)
  - Fix a potential tsd cleanup leak.  (@cferris1000, @jasone)
  - Fix run quantization.  In practice this bug had no impact unless
    applications requested memory with alignment exceeding one page.
    (@jasone, @djwatson)
  - Fix LinuxThreads-specific bootstrapping deadlock.  (Cosmin Paraschiv)
  - jeprof:
    + Don't discard curl options if timeout is not defined.  (@djwatson)
    + Detect failed profile fetches.  (@djwatson)
  - Fix stats.arenas.<i>.{dss,lg_dirty_mult,decay_time,pactive,pdirty} for
    --disable-stats case.  (@jasone)

* 4.0.4 (October 24, 2015)

  This bugfix release fixes another xallocx() regression.  No other regressions
  have come to light in over a month, so this is likely a good starting point
  for people who prefer to wait for "dot one" releases with all the major issues
  shaken out.

  Bug fixes:
  - Fix xallocx(..., MALLOCX_ZERO to zero the last full trailing page of large
    allocations that have been randomly assigned an offset of 0 when
    --enable-cache-oblivious configure option is enabled.

* 4.0.3 (September 24, 2015)

  This bugfix release continues the trend of xallocx() and heap profiling fixes.

  Bug fixes:
  - Fix xallocx(..., MALLOCX_ZERO) to zero all trailing bytes of large
    allocations when --enable-cache-oblivious configure option is enabled.
  - Fix xallocx(..., MALLOCX_ZERO) to zero trailing bytes of huge allocations
    when resizing from/to a size class that is not a multiple of the chunk size.
  - Fix prof_tctx_dump_iter() to filter out nodes that were created after heap
    profile dumping started.
  - Work around a potentially bad thread-specific data initialization
    interaction with NPTL (glibc's pthreads implementation).

* 4.0.2 (September 21, 2015)

  This bugfix release addresses a few bugs specific to heap profiling.

  Bug fixes:
  - Fix ixallocx_prof_sample() to never modify nor create sampled small
    allocations.  xallocx() is in general incapable of moving small allocations,
    so this fix removes buggy code without loss of generality.
  - Fix irallocx_prof_sample() to always allocate large regions, even when
    alignment is non-zero.
  - Fix prof_alloc_rollback() to read tdata from thread-specific data rather
    than dereferencing a potentially invalid tctx.

* 4.0.1 (September 15, 2015)

  This is a bugfix release that is somewhat high risk due to the amount of
  refactoring required to address deep xallocx() problems.  As a side effect of
  these fixes, xallocx() now tries harder to partially fulfill requests for
  optional extra space.  Note that a couple of minor heap profiling
  optimizations are included, but these are better thought of as performance
  fixes that were integral to disovering most of the other bugs.

  Optimizations:
  - Avoid a chunk metadata read in arena_prof_tctx_set(), since it is in the
    fast path when heap profiling is enabled.  Additionally, split a special
    case out into arena_prof_tctx_reset(), which also avoids chunk metadata
    reads.
  - Optimize irallocx_prof() to optimistically update the sampler state.  The
    prior implementation appears to have been a holdover from when
    rallocx()/xallocx() functionality was combined as rallocm().

  Bug fixes:
  - Fix TLS configuration such that it is enabled by default for platforms on
    which it works correctly.
  - Fix arenas_cache_cleanup() and arena_get_hard() to handle
    allocation/deallocation within the application's thread-specific data
    cleanup functions even after arenas_cache is torn down.
  - Fix xallocx() bugs related to size+extra exceeding HUGE_MAXCLASS.
  - Fix chunk purge hook calls for in-place huge shrinking reallocation to
    specify the old chunk size rather than the new chunk size.  This bug caused
    no correctness issues for the default chunk purge function, but was
    visible to custom functions set via the "arena.<i>.chunk_hooks" mallctl.
  - Fix heap profiling bugs:
    + Fix heap profiling to distinguish among otherwise identical sample sites
      with interposed resets (triggered via the "prof.reset" mallctl).  This bug
      could cause data structure corruption that would most likely result in a
      segfault.
    + Fix irealloc_prof() to prof_alloc_rollback() on OOM.
    + Make one call to prof_active_get_unlocked() per allocation event, and use
      the result throughout the relevant functions that handle an allocation
      event.  Also add a missing check in prof_realloc().  These fixes protect
      allocation events against concurrent prof_active changes.
    + Fix ixallocx_prof() to pass usize_max and zero to ixallocx_prof_sample()
      in the correct order.
    + Fix prof_realloc() to call prof_free_sampled_object() after calling
      prof_malloc_sample_object().  Prior to this fix, if tctx and old_tctx were
      the same, the tctx could have been prematurely destroyed.
  - Fix portability bugs:
    + Don't bitshift by negative amounts when encoding/decoding run sizes in
      chunk header maps.  This affected systems with page sizes greater than 8
      KiB.
    + Rename index_t to szind_t to avoid an existing type on Solaris.
    + Add JEMALLOC_CXX_THROW to the memalign() function prototype, in order to
      match glibc and avoid compilation errors when including both
      jemalloc/jemalloc.h and malloc.h in C++ code.
    + Don't assume that /bin/sh is appropriate when running size_classes.sh
      during configuration.
    + Consider __sparcv9 a synonym for __sparc64__ when defining LG_QUANTUM.
    + Link tests to librt if it contains clock_gettime(2).

* 4.0.0 (August 17, 2015)

  This version contains many speed and space optimizations, both minor and
  major.  The major themes are generalization, unification, and simplification.
  Although many of these optimizations cause no visible behavior change, their
  cumulative effect is substantial.

  New features:
  - Normalize size class spacing to be consistent across the complete size
    range.  By default there are four size classes per size doubling, but this
    is now configurable via the --with-lg-size-class-group option.  Also add the
    --with-lg-page, --with-lg-page-sizes, --with-lg-quantum, and
    --with-lg-tiny-min options, which can be used to tweak page and size class
    settings.  Impacts:
    + Worst case performance for incrementally growing/shrinking reallocation
      is improved because there are far fewer size classes, and therefore
      copying happens less often.
    + Internal fragmentation is limited to 20% for all but the smallest size
      classes (those less than four times the quantum).  (1B + 4 KiB)
      and (1B + 4 MiB) previously suffered nearly 50% internal fragmentation.
    + Chunk fragmentation tends to be lower because there are fewer distinct run
      sizes to pack.
  - Add support for explicit tcaches.  The "tcache.create", "tcache.flush", and
    "tcache.destroy" mallctls control tcache lifetime and flushing, and the
    MALLOCX_TCACHE(tc) and MALLOCX_TCACHE_NONE flags to the *allocx() API
    control which tcache is used for each operation.
  - Implement per thread heap profiling, as well as the ability to
    enable/disable heap profiling on a per thread basis.  Add the "prof.reset",
    "prof.lg_sample", "thread.prof.name", "thread.prof.active",
    "opt.prof_thread_active_init", "prof.thread_active_init", and
    "thread.prof.active" mallctls.
  - Add support for per arena application-specified chunk allocators, configured
    via the "arena.<i>.chunk_hooks" mallctl.
  - Refactor huge allocation to be managed by arenas, so that arenas now
    function as general purpose independent allocators.  This is important in
    the context of user-specified chunk allocators, aside from the scalability
    benefits.  Related new statistics:
    + The "stats.arenas.<i>.huge.allocated", "stats.arenas.<i>.huge.nmalloc",
      "stats.arenas.<i>.huge.ndalloc", and "stats.arenas.<i>.huge.nrequests"
      mallctls provide high level per arena huge allocation statistics.
    + The "arenas.nhchunks", "arenas.hchunk.<i>.size",
      "stats.arenas.<i>.hchunks.<j>.nmalloc",
      "stats.arenas.<i>.hchunks.<j>.ndalloc",
      "stats.arenas.<i>.hchunks.<j>.nrequests", and
      "stats.arenas.<i>.hchunks.<j>.curhchunks" mallctls provide per size class
      statistics.
  - Add the 'util' column to malloc_stats_print() output, which reports the
    proportion of available regions that are currently in use for each small
    size class.
  - Add "alloc" and "free" modes for for junk filling (see the "opt.junk"
    mallctl), so that it is possible to separately enable junk filling for
    allocation versus deallocation.
  - Add the jemalloc-config script, which provides information about how
    jemalloc was configured, and how to integrate it into application builds.
  - Add metadata statistics, which are accessible via the "stats.metadata",
    "stats.arenas.<i>.metadata.mapped", and
    "stats.arenas.<i>.metadata.allocated" mallctls.
  - Add the "stats.resident" mallctl, which reports the upper limit of
    physically resident memory mapped by the allocator.
  - Add per arena control over unused dirty page purging, via the
    "arenas.lg_dirty_mult", "arena.<i>.lg_dirty_mult", and
    "stats.arenas.<i>.lg_dirty_mult" mallctls.
  - Add the "prof.gdump" mallctl, which makes it possible to toggle the gdump
    feature on/off during program execution.
  - Add sdallocx(), which implements sized deallocation.  The primary
    optimization over dallocx() is the removal of a metadata read, which often
    suffers an L1 cache miss.
  - Add missing header includes in jemalloc/jemalloc.h, so that applications
    only have to #include <jemalloc/jemalloc.h>.
  - Add support for additional platforms:
    + Bitrig
    + Cygwin
    + DragonFlyBSD
    + iOS
    + OpenBSD
    + OpenRISC/or1k

  Optimizations:
  - Maintain dirty runs in per arena LRUs rather than in per arena trees of
    dirty-run-containing chunks.  In practice this change significantly reduces
    dirty page purging volume.
  - Integrate whole chunks into the unused dirty page purging machinery.  This
    reduces the cost of repeated huge allocation/deallocation, because it
    effectively introduces a cache of chunks.
  - Split the arena chunk map into two separate arrays, in order to increase
    cache locality for the frequently accessed bits.
  - Move small run metadata out of runs, into arena chunk headers.  This reduces
    run fragmentation, smaller runs reduce external fragmentation for small size
    classes, and packed (less uniformly aligned) metadata layout improves CPU
    cache set distribution.
  - Randomly distribute large allocation base pointer alignment relative to page
    boundaries in order to more uniformly utilize CPU cache sets.  This can be
    disabled via the --disable-cache-oblivious configure option, and queried via
    the "config.cache_oblivious" mallctl.
  - Micro-optimize the fast paths for the public API functions.
  - Refactor thread-specific data to reside in a single structure.  This assures
    that only a single TLS read is necessary per call into the public API.
  - Implement in-place huge allocation growing and shrinking.
  - Refactor rtree (radix tree for chunk lookups) to be lock-free, and make
    additional optimizations that reduce maximum lookup depth to one or two
    levels.  This resolves what was a concurrency bottleneck for per arena huge
    allocation, because a global data structure is critical for determining
    which arenas own which huge allocations.

  Incompatible changes:
  - Replace --enable-cc-silence with --disable-cc-silence to suppress spurious
    warnings by default.
  - Assure that the constness of malloc_usable_size()'s return type matches that
    of the system implementation.
  - Change the heap profile dump format to support per thread heap profiling,
    rename pprof to jeprof, and enhance it with the --thread=<n> option.  As a
    result, the bundled jeprof must now be used rather than the upstream
    (gperftools) pprof.
  - Disable "opt.prof_final" by default, in order to avoid atexit(3), which can
    internally deadlock on some platforms.
  - Change the "arenas.nlruns" mallctl type from size_t to unsigned.
  - Replace the "stats.arenas.<i>.bins.<j>.allocated" mallctl with
    "stats.arenas.<i>.bins.<j>.curregs".
  - Ignore MALLOC_CONF in set{uid,gid,cap} binaries.
  - Ignore MALLOCX_ARENA(a) in dallocx(), in favor of using the
    MALLOCX_TCACHE(tc) and MALLOCX_TCACHE_NONE flags to control tcache usage.

  Removed features:
  - Remove the *allocm() API, which is superseded by the *allocx() API.
  - Remove the --enable-dss options, and make dss non-optional on all platforms
    which support sbrk(2).
  - Remove the "arenas.purge" mallctl, which was obsoleted by the
    "arena.<i>.purge" mallctl in 3.1.0.
  - Remove the unnecessary "opt.valgrind" mallctl; jemalloc automatically
    detects whether it is running inside Valgrind.
  - Remove the "stats.huge.allocated", "stats.huge.nmalloc", and
    "stats.huge.ndalloc" mallctls.
  - Remove the --enable-mremap option.
  - Remove the "stats.chunks.current", "stats.chunks.total", and
    "stats.chunks.high" mallctls.

  Bug fixes:
  - Fix the cactive statistic to decrease (rather than increase) when active
    memory decreases.  This regression was first released in 3.5.0.
  - Fix OOM handling in memalign() and valloc().  A variant of this bug existed
    in all releases since 2.0.0, which introduced these functions.
  - Fix an OOM-related regression in arena_tcache_fill_small(), which could
    cause cache corruption on OOM.  This regression was present in all releases
    from 2.2.0 through 3.6.0.
  - Fix size class overflow handling for malloc(), posix_memalign(), memalign(),
    calloc(), and realloc() when profiling is enabled.
  - Fix the "arena.<i>.dss" mallctl to return an error if "primary" or
    "secondary" precedence is specified, but sbrk(2) is not supported.
  - Fix fallback lg_floor() implementations to handle extremely large inputs.
  - Ensure the default purgeable zone is after the default zone on OS X.
  - Fix latent bugs in atomic_*().
  - Fix the "arena.<i>.dss" mallctl to handle read-only calls.
  - Fix tls_model configuration to enable the initial-exec model when possible.
  - Mark malloc_conf as a weak symbol so that the application can override it.
  - Correctly detect glibc's adaptive pthread mutexes.
  - Fix the --without-export configure option.

* 3.6.0 (March 31, 2014)

  This version contains a critical bug fix for a regression present in 3.5.0 and
  3.5.1.

  Bug fixes:
  - Fix a regression in arena_chunk_alloc() that caused crashes during
    small/large allocation if chunk allocation failed.  In the absence of this
    bug, chunk allocation failure would result in allocation failure, e.g.  NULL
    return from malloc().  This regression was introduced in 3.5.0.
  - Fix backtracing for gcc intrinsics-based backtracing by specifying
    -fno-omit-frame-pointer to gcc.  Note that the application (and all the
    libraries it links to) must also be compiled with this option for
    backtracing to be reliable.
  - Use dss allocation precedence for huge allocations as well as small/large
    allocations.
  - Fix test assertion failure message formatting.  This bug did not manifest on
    x86_64 systems because of implementation subtleties in va_list.
  - Fix inconsequential test failures for hash and SFMT code.

  New features:
  - Support heap profiling on FreeBSD.  This feature depends on the proc
    filesystem being mounted during heap profile dumping.

* 3.5.1 (February 25, 2014)

  This version primarily addresses minor bugs in test code.

  Bug fixes:
  - Configure Solaris/Illumos to use MADV_FREE.
  - Fix junk filling for mremap(2)-based huge reallocation.  This is only
    relevant if configuring with the --enable-mremap option specified.
  - Avoid compilation failure if 'restrict' C99 keyword is not supported by the
    compiler.
  - Add a configure test for SSE2 rather than assuming it is usable on i686
    systems.  This fixes test compilation errors, especially on 32-bit Linux
    systems.
  - Fix mallctl argument size mismatches (size_t vs. uint64_t) in the stats unit
    test.
  - Fix/remove flawed alignment-related overflow tests.
  - Prevent compiler optimizations that could change backtraces in the
    prof_accum unit test.

* 3.5.0 (January 22, 2014)

  This version focuses on refactoring and automated testing, though it also
  includes some non-trivial heap profiling optimizations not mentioned below.

  New features:
  - Add the *allocx() API, which is a successor to the experimental *allocm()
    API.  The *allocx() functions are slightly simpler to use because they have
    fewer parameters, they directly return the results of primary interest, and
    mallocx()/rallocx() avoid the strict aliasing pitfall that
    allocm()/rallocm() share with posix_memalign().  Note that *allocm() is
    slated for removal in the next non-bugfix release.
  - Add support for LinuxThreads.

  Bug fixes:
  - Unless heap profiling is enabled, disable floating point code and don't link
    with libm.  This, in combination with e.g. EXTRA_CFLAGS=-mno-sse on x64
    systems, makes it possible to completely disable floating point register
    use.  Some versions of glibc neglect to save/restore caller-saved floating
    point registers during dynamic lazy symbol loading, and the symbol loading
    code uses whatever malloc the application happens to have linked/loaded
    with, the result being potential floating point register corruption.
  - Report ENOMEM rather than EINVAL if an OOM occurs during heap profiling
    backtrace creation in imemalign().  This bug impacted posix_memalign() and
    aligned_alloc().
  - Fix a file descriptor leak in a prof_dump_maps() error path.
  - Fix prof_dump() to close the dump file descriptor for all relevant error
    paths.
  - Fix rallocm() to use the arena specified by the ALLOCM_ARENA(s) flag for
    allocation, not just deallocation.
  - Fix a data race for large allocation stats counters.
  - Fix a potential infinite loop during thread exit.  This bug occurred on
    Solaris, and could affect other platforms with similar pthreads TSD
    implementations.
  - Don't junk-fill reallocations unless usable size changes.  This fixes a
    violation of the *allocx()/*allocm() semantics.
  - Fix growing large reallocation to junk fill new space.
  - Fix huge deallocation to junk fill when munmap is disabled.
  - Change the default private namespace prefix from empty to je_, and change
    --with-private-namespace-prefix so that it prepends an additional prefix
    rather than replacing je_.  This reduces the likelihood of applications
    which statically link jemalloc experiencing symbol name collisions.
  - Add missing private namespace mangling (relevant when
    --with-private-namespace is specified).
  - Add and use JEMALLOC_INLINE_C so that static inline functions are marked as
    static even for debug builds.
  - Add a missing mutex unlock in a malloc_init_hard() error path.  In practice
    this error path is never executed.
  - Fix numerous bugs in malloc_strotumax() error handling/reporting.  These
    bugs had no impact except for malformed inputs.
  - Fix numerous bugs in malloc_snprintf().  These bugs were not exercised by
    existing calls, so they had no impact.

* 3.4.1 (October 20, 2013)

  Bug fixes:
  - Fix a race in the "arenas.extend" mallctl that could cause memory corruption
    of internal data structures and subsequent crashes.
  - Fix Valgrind integration flaws that caused Valgrind warnings about reads of
    uninitialized memory in:
    + arena chunk headers
    + internal zero-initialized data structures (relevant to tcache and prof
      code)
  - Preserve errno during the first allocation.  A readlink(2) call during
    initialization fails unless /etc/malloc.conf exists, so errno was typically
    set during the first allocation prior to this fix.
  - Fix compilation warnings reported by gcc 4.8.1.

* 3.4.0 (June 2, 2013)

  This version is essentially a small bugfix release, but the addition of
  aarch64 support requires that the minor version be incremented.

  Bug fixes:
  - Fix race-triggered deadlocks in chunk_record().  These deadlocks were
    typically triggered by multiple threads concurrently deallocating huge
    objects.

  New features:
  - Add support for the aarch64 architecture.

* 3.3.1 (March 6, 2013)

  This version fixes bugs that are typically encountered only when utilizing
  custom run-time options.

  Bug fixes:
  - Fix a locking order bug that could cause deadlock during fork if heap
    profiling were enabled.
  - Fix a chunk recycling bug that could cause the allocator to lose track of
    whether a chunk was zeroed.  On FreeBSD, NetBSD, and OS X, it could cause
    corruption if allocating via sbrk(2) (unlikely unless running with the
    "dss:primary" option specified).  This was completely harmless on Linux
    unless using mlockall(2) (and unlikely even then, unless the
    --disable-munmap configure option or the "dss:primary" option was
    specified).  This regression was introduced in 3.1.0 by the
    mlockall(2)/madvise(2) interaction fix.
  - Fix TLS-related memory corruption that could occur during thread exit if the
    thread never allocated memory.  Only the quarantine and prof facilities were
    susceptible.
  - Fix two quarantine bugs:
    + Internal reallocation of the quarantined object array leaked the old
      array.
    + Reallocation failure for internal reallocation of the quarantined object
      array (very unlikely) resulted in memory corruption.
  - Fix Valgrind integration to annotate all internally allocated memory in a
    way that keeps Valgrind happy about internal data structure access.
  - Fix building for s390 systems.

* 3.3.0 (January 23, 2013)

  This version includes a few minor performance improvements in addition to the
  listed new features and bug fixes.

  New features:
  - Add clipping support to lg_chunk option processing.
  - Add the --enable-ivsalloc option.
  - Add the --without-export option.
  - Add the --disable-zone-allocator option.

  Bug fixes:
  - Fix "arenas.extend" mallctl to output the number of arenas.
  - Fix chunk_recycle() to unconditionally inform Valgrind that returned memory
    is undefined.
  - Fix build break on FreeBSD related to alloca.h.

* 3.2.0 (November 9, 2012)

  In addition to a couple of bug fixes, this version modifies page run
  allocation and dirty page purging algorithms in order to better control
  page-level virtual memory fragmentation.

  Incompatible changes:
  - Change the "opt.lg_dirty_mult" default from 5 to 3 (32:1 to 8:1).

  Bug fixes:
  - Fix dss/mmap allocation precedence code to use recyclable mmap memory only
    after primary dss allocation fails.
  - Fix deadlock in the "arenas.purge" mallctl.  This regression was introduced
    in 3.1.0 by the addition of the "arena.<i>.purge" mallctl.

* 3.1.0 (October 16, 2012)

  New features:
  - Auto-detect whether running inside Valgrind, thus removing the need to
    manually specify MALLOC_CONF=valgrind:true.
  - Add the "arenas.extend" mallctl, which allows applications to create
    manually managed arenas.
  - Add the ALLOCM_ARENA() flag for {,r,d}allocm().
  - Add the "opt.dss", "arena.<i>.dss", and "stats.arenas.<i>.dss" mallctls,
    which provide control over dss/mmap precedence.
  - Add the "arena.<i>.purge" mallctl, which obsoletes "arenas.purge".
  - Define LG_QUANTUM for hppa.

  Incompatible changes:
  - Disable tcache by default if running inside Valgrind, in order to avoid
    making unallocated objects appear reachable to Valgrind.
  - Drop const from malloc_usable_size() argument on Linux.

  Bug fixes:
  - Fix heap profiling crash if sampled object is freed via realloc(p, 0).
  - Remove const from __*_hook variable declarations, so that glibc can modify
    them during process forking.
  - Fix mlockall(2)/madvise(2) interaction.
  - Fix fork(2)-related deadlocks.
  - Fix error return value for "thread.tcache.enabled" mallctl.

* 3.0.0 (May 11, 2012)

  Although this version adds some major new features, the primary focus is on
  internal code cleanup that facilitates maintainability and portability, most
  of which is not reflected in the ChangeLog.  This is the first release to
  incorporate substantial contributions from numerous other developers, and the
  result is a more broadly useful allocator (see the git revision history for
  contribution details).  Note that the license has been unified, thanks to
  Facebook granting a license under the same terms as the other copyright
  holders (see COPYING).

  New features:
  - Implement Valgrind support, redzones, and quarantine.
  - Add support for additional platforms:
    + FreeBSD
    + Mac OS X Lion
    + MinGW
    + Windows (no support yet for replacing the system malloc)
  - Add support for additional architectures:
    + MIPS
    + SH4
    + Tilera
  - Add support for cross compiling.
  - Add nallocm(), which rounds a request size up to the nearest size class
    without actually allocating.
  - Implement aligned_alloc() (blame C11).
  - Add the "thread.tcache.enabled" mallctl.
  - Add the "opt.prof_final" mallctl.
  - Update pprof (from gperftools 2.0).
  - Add the --with-mangling option.
  - Add the --disable-experimental option.
  - Add the --disable-munmap option, and make it the default on Linux.
  - Add the --enable-mremap option, which disables use of mremap(2) by default.

  Incompatible changes:
  - Enable stats by default.
  - Enable fill by default.
  - Disable lazy locking by default.
  - Rename the "tcache.flush" mallctl to "thread.tcache.flush".
  - Rename the "arenas.pagesize" mallctl to "arenas.page".
  - Change the "opt.lg_prof_sample" default from 0 to 19 (1 B to 512 KiB).
  - Change the "opt.prof_accum" default from true to false.

  Removed features:
  - Remove the swap feature, including the "config.swap", "swap.avail",
    "swap.prezeroed", "swap.nfds", and "swap.fds" mallctls.
  - Remove highruns statistics, including the
    "stats.arenas.<i>.bins.<j>.highruns" and
    "stats.arenas.<i>.lruns.<j>.highruns" mallctls.
  - As part of small size class refactoring, remove the "opt.lg_[qc]space_max",
    "arenas.cacheline", "arenas.subpage", "arenas.[tqcs]space_{min,max}", and
    "arenas.[tqcs]bins" mallctls.
  - Remove the "arenas.chunksize" mallctl.
  - Remove the "opt.lg_prof_tcmax" option.
  - Remove the "opt.lg_prof_bt_max" option.
  - Remove the "opt.lg_tcache_gc_sweep" option.
  - Remove the --disable-tiny option, including the "config.tiny" mallctl.
  - Remove the --enable-dynamic-page-shift configure option.
  - Remove the --enable-sysv configure option.

  Bug fixes:
  - Fix a statistics-related bug in the "thread.arena" mallctl that could cause
    invalid statistics and crashes.
  - Work around TLS deallocation via free() on Linux.  This bug could cause
    write-after-free memory corruption.
  - Fix a potential deadlock that could occur during interval- and
    growth-triggered heap profile dumps.
  - Fix large calloc() zeroing bugs due to dropping chunk map unzeroed flags.
  - Fix chunk_alloc_dss() to stop claiming memory is zeroed.  This bug could
    cause memory corruption and crashes with --enable-dss specified.
  - Fix fork-related bugs that could cause deadlock in children between fork
    and exec.
  - Fix malloc_stats_print() to honor 'b' and 'l' in the opts parameter.
  - Fix realloc(p, 0) to act like free(p).
  - Do not enforce minimum alignment in memalign().
  - Check for NULL pointer in malloc_usable_size().
  - Fix an off-by-one heap profile statistics bug that could be observed in
    interval- and growth-triggered heap profiles.
  - Fix the "epoch" mallctl to update cached stats even if the passed in epoch
    is 0.
  - Fix bin->runcur management to fix a layout policy bug.  This bug did not
    affect correctness.
  - Fix a bug in choose_arena_hard() that potentially caused more arenas to be
    initialized than necessary.
  - Add missing "opt.lg_tcache_max" mallctl implementation.
  - Use glibc allocator hooks to make mixed allocator usage less likely.
  - Fix build issues for --disable-tcache.
  - Don't mangle pthread_create() when --with-private-namespace is specified.

* 2.2.5 (November 14, 2011)

  Bug fixes:
  - Fix huge_ralloc() race when using mremap(2).  This is a serious bug that
    could cause memory corruption and/or crashes.
  - Fix huge_ralloc() to maintain chunk statistics.
  - Fix malloc_stats_print(..., "a") output.

* 2.2.4 (November 5, 2011)

  Bug fixes:
  - Initialize arenas_tsd before using it.  This bug existed for 2.2.[0-3], as
    well as for --disable-tls builds in earlier releases.
  - Do not assume a 4 KiB page size in test/rallocm.c.

* 2.2.3 (August 31, 2011)

  This version fixes numerous bugs related to heap profiling.

  Bug fixes:
  - Fix a prof-related race condition.  This bug could cause memory corruption,
    but only occurred in non-default configurations (prof_accum:false).
  - Fix off-by-one backtracing issues (make sure that prof_alloc_prep() is
    excluded from backtraces).
  - Fix a prof-related bug in realloc() (only triggered by OOM errors).
  - Fix prof-related bugs in allocm() and rallocm().
  - Fix prof_tdata_cleanup() for --disable-tls builds.
  - Fix a relative include path, to fix objdir builds.

* 2.2.2 (July 30, 2011)

  Bug fixes:
  - Fix a build error for --disable-tcache.
  - Fix assertions in arena_purge() (for real this time).
  - Add the --with-private-namespace option.  This is a workaround for symbol
    conflicts that can inadvertently arise when using static libraries.

* 2.2.1 (March 30, 2011)

  Bug fixes:
  - Implement atomic operations for x86/x64.  This fixes compilation failures
    for versions of gcc that are still in wide use.
  - Fix an assertion in arena_purge().

* 2.2.0 (March 22, 2011)

  This version incorporates several improvements to algorithms and data
  structures that tend to reduce fragmentation and increase speed.

  New features:
  - Add the "stats.cactive" mallctl.
  - Update pprof (from google-perftools 1.7).
  - Improve backtracing-related configuration logic, and add the
    --disable-prof-libgcc option.

  Bug fixes:
  - Change default symbol visibility from "internal", to "hidden", which
    decreases the overhead of library-internal function calls.
  - Fix symbol visibility so that it is also set on OS X.
  - Fix a build dependency regression caused by the introduction of the .pic.o
    suffix for PIC object files.
  - Add missing checks for mutex initialization failures.
  - Don't use libgcc-based backtracing except on x64, where it is known to work.
  - Fix deadlocks on OS X that were due to memory allocation in
    pthread_mutex_lock().
  - Heap profiling-specific fixes:
    + Fix memory corruption due to integer overflow in small region index
      computation, when using a small enough sample interval that profiling
      context pointers are stored in small run headers.
    + Fix a bootstrap ordering bug that only occurred with TLS disabled.
    + Fix a rallocm() rsize bug.
    + Fix error detection bugs for aligned memory allocation.

* 2.1.3 (March 14, 2011)

  Bug fixes:
  - Fix a cpp logic regression (due to the "thread.{de,}allocatedp" mallctl fix
    for OS X in 2.1.2).
  - Fix a "thread.arena" mallctl bug.
  - Fix a thread cache stats merging bug.

* 2.1.2 (March 2, 2011)

  Bug fixes:
  - Fix "thread.{de,}allocatedp" mallctl for OS X.
  - Add missing jemalloc.a to build system.

* 2.1.1 (January 31, 2011)

  Bug fixes:
  - Fix aligned huge reallocation (affected allocm()).
  - Fix the ALLOCM_LG_ALIGN macro definition.
  - Fix a heap dumping deadlock.
  - Fix a "thread.arena" mallctl bug.

* 2.1.0 (December 3, 2010)

  This version incorporates some optimizations that can't quite be considered
  bug fixes.

  New features:
  - Use Linux's mremap(2) for huge object reallocation when possible.
  - Avoid locking in mallctl*() when possible.
  - Add the "thread.[de]allocatedp" mallctl's.
  - Convert the manual page source from roff to DocBook, and generate both roff
    and HTML manuals.

  Bug fixes:
  - Fix a crash due to incorrect bootstrap ordering.  This only impacted
    --enable-debug --enable-dss configurations.
  - Fix a minor statistics bug for mallctl("swap.avail", ...).

* 2.0.1 (October 29, 2010)

  Bug fixes:
  - Fix a race condition in heap profiling that could cause undefined behavior
    if "opt.prof_accum" were disabled.
  - Add missing mutex unlocks for some OOM error paths in the heap profiling
    code.
  - Fix a compilation error for non-C99 builds.

* 2.0.0 (October 24, 2010)

  This version focuses on the experimental *allocm() API, and on improved
  run-time configuration/introspection.  Nonetheless, numerous performance
  improvements are also included.

  New features:
  - Implement the experimental {,r,s,d}allocm() API, which provides a superset
    of the functionality available via malloc(), calloc(), posix_memalign(),
    realloc(), malloc_usable_size(), and free().  These functions can be used to
    allocate/reallocate aligned zeroed memory, ask for optional extra memory
    during reallocation, prevent object movement during reallocation, etc.
  - Replace JEMALLOC_OPTIONS/JEMALLOC_PROF_PREFIX with MALLOC_CONF, which is
    more human-readable, and more flexible.  For example:
      JEMALLOC_OPTIONS=AJP
    is now:
      MALLOC_CONF=abort:true,fill:true,stats_print:true
  - Port to Apple OS X.  Sponsored by Mozilla.
  - Make it possible for the application to control thread-->arena mappings via
    the "thread.arena" mallctl.
  - Add compile-time support for all TLS-related functionality via pthreads TSD.
    This is mainly of interest for OS X, which does not support TLS, but has a
    TSD implementation with similar performance.
  - Override memalign() and valloc() if they are provided by the system.
  - Add the "arenas.purge" mallctl, which can be used to synchronously purge all
    dirty unused pages.
  - Make cumulative heap profiling data optional, so that it is possible to
    limit the amount of memory consumed by heap profiling data structures.
  - Add per thread allocation counters that can be accessed via the
    "thread.allocated" and "thread.deallocated" mallctls.

  Incompatible changes:
  - Remove JEMALLOC_OPTIONS and malloc_options (see MALLOC_CONF above).
  - Increase default backtrace depth from 4 to 128 for heap profiling.
  - Disable interval-based profile dumps by default.

  Bug fixes:
  - Remove bad assertions in fork handler functions.  These assertions could
    cause aborts for some combinations of configure settings.
  - Fix strerror_r() usage to deal with non-standard semantics in GNU libc.
  - Fix leak context reporting.  This bug tended to cause the number of contexts
    to be underreported (though the reported number of objects and bytes were
    correct).
  - Fix a realloc() bug for large in-place growing reallocation.  This bug could
    cause memory corruption, but it was hard to trigger.
  - Fix an allocation bug for small allocations that could be triggered if
    multiple threads raced to create a new run of backing pages.
  - Enhance the heap profiler to trigger samples based on usable size, rather
    than request size.
  - Fix a heap profiling bug due to sometimes losing track of requested object
    size for sampled objects.

* 1.0.3 (August 12, 2010)

  Bug fixes:
  - Fix the libunwind-based implementation of stack backtracing (used for heap
    profiling).  This bug could cause zero-length backtraces to be reported.
  - Add a missing mutex unlock in library initialization code.  If multiple
    threads raced to initialize malloc, some of them could end up permanently
    blocked.

* 1.0.2 (May 11, 2010)

  Bug fixes:
  - Fix junk filling of large objects, which could cause memory corruption.
  - Add MAP_NORESERVE support for chunk mapping, because otherwise virtual
    memory limits could cause swap file configuration to fail.  Contributed by
    Jordan DeLong.

* 1.0.1 (April 14, 2010)

  Bug fixes:
  - Fix compilation when --enable-fill is specified.
  - Fix threads-related profiling bugs that affected accuracy and caused memory
    to be leaked during thread exit.
  - Fix dirty page purging race conditions that could cause crashes.
  - Fix crash in tcache flushing code during thread destruction.

* 1.0.0 (April 11, 2010)

  This release focuses on speed and run-time introspection.  Numerous
  algorithmic improvements make this release substantially faster than its
  predecessors.

  New features:
  - Implement autoconf-based configuration system.
  - Add mallctl*(), for the purposes of introspection and run-time
    configuration.
  - Make it possible for the application to manually flush a thread's cache, via
    the "tcache.flush" mallctl.
  - Base maximum dirty page count on proportion of active memory.
  - Compute various additional run-time statistics, including per size class
    statistics for large objects.
  - Expose malloc_stats_print(), which can be called repeatedly by the
    application.
  - Simplify the malloc_message() signature to only take one string argument,
    and incorporate an opaque data pointer argument for use by the application
    in combination with malloc_stats_print().
  - Add support for allocation backed by one or more swap files, and allow the
    application to disable over-commit if swap files are in use.
  - Implement allocation profiling and leak checking.

  Removed features:
  - Remove the dynamic arena rebalancing code, since thread-specific caching
    reduces its utility.

  Bug fixes:
  - Modify chunk allocation to work when address space layout randomization
    (ASLR) is in use.
  - Fix thread cleanup bugs related to TLS destruction.
  - Handle 0-size allocation requests in posix_memalign().
  - Fix a chunk leak.  The leaked chunks were never touched, so this impacted
    virtual memory usage, but not physical memory usage.

* linux_2008082[78]a (August 27/28, 2008)

  These snapshot releases are the simple result of incorporating Linux-specific
  support into the FreeBSD malloc sources.

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