Many mallctl*() end points require no locking, so push the locking down
to just the functions that need it. This is of particular import for
"thread.allocated" and "thread.deallocated", which are intended as a
low-overhead way to introspect per thread allocation activity.
Replace the single-character run-time flags with key/value pairs, which
can be set via the malloc_conf global, /etc/malloc.conf, and the
MALLOC_CONF environment variable.
Replace the JEMALLOC_PROF_PREFIX environment variable with the
"opt.prof_prefix" option.
Replace umax2s() with u2s().
Add the "thread.allocated" and "thread.deallocated" mallctls, which can
be used to query the total number of bytes ever allocated/deallocated by
the calling thread.
Add s2u() and sa2u(), which can be used to compute the usable size that
will result from an allocation request of a particular size/alignment.
Re-factor ipalloc() to use sa2u().
Enhance the heap profiler to trigger samples based on usable size,
rather than request size. This has a subtle, but important, impact on
the accuracy of heap sampling. For example, previous to this change,
16- and 17-byte objects were sampled at nearly the same rate, but
17-byte objects actually consume 32 bytes each. Therefore it was
possible for the sample to be somewhat skewed compared to actual memory
usage of the allocated objects.
Add the R option to control whether cumulative heap profile data
are maintained. Add the T option to control the size of per thread
backtrace caches, primarily because when the R option is specified,
backtraces that no longer have allocations associated with them are
discarded as soon as no thread caches refer to them.
Add the E/e options to control whether the application starts with
sampling active/inactive (secondary control to F/f). Add the
prof.active mallctl so that the application can activate/deactivate
sampling on the fly.
Make it possible to disable interval-triggered profile dumping, even if
profiling is enabled. This is useful if the user only wants a single
dump at exit, or if the application manually triggers profile dumps.
Remove medium size classes, because concurrent dirty page purging is
no longer capable of purging inactive dirty pages inside active runs
(due to recent arena/bin locking changes).
Enhance tcache to support caching large objects, so that the same range
of size classes is still cached, despite the removal of medium size
class support.
For bin-related allocation, protect data structures with bin locks
rather than arena locks. Arena locks remain for run
allocation/deallocation and other miscellaneous operations.
Restructure statistics counters to maintain per bin
allocated/nmalloc/ndalloc, but continue to provide arena-wide statistics
via aggregation in the ctl code.
Use chains of cached objects, rather than using arrays of pointers.
Since tcache_bin_t is no longer dynamically sized, convert tcache_t's
tbin to an array of structures, rather than an array of pointers. This
implicitly removes tcache_bin_{create,destroy}(), which further
simplifies the fast path for malloc/free.
Use cacheline alignment for tcache_t allocations.
Remove runtime configuration option for number of tcache bin slots, and
replace it with a boolean option for enabling/disabling tcache.
Limit the number of tcache objects to the lesser of TCACHE_NSLOTS_MAX
and 2X the number of regions per run for the size class.
For GC-triggered flush, discard 3/4 of the objects below the low water
mark, rather than 1/2.
