Reduce rtree memory usage by storing booleans (1 byte each) rather than
pointers. The rtree code is only used to record whether jemalloc manages
a chunk of memory, so there's no need to store pointers in the rtree.
Increase rtree node size to 64 KiB in order to reduce tree depth from 13
to 3 on 64-bit systems. The conversion to more compact leaf nodes was
enough by itself to make the rtree depth 1 on 32-bit systems; due to the
fact that root nodes are smaller than the specified node size if
possible, the node size change has no impact on 32-bit systems (assuming
default chunk size).
Add a library constructor for jemalloc that initializes the allocator.
This fixes a race that could occur if threads were created by the main
thread prior to any memory allocation, followed by fork(2), and then
memory allocation in the child process.
Fix the prefork/postfork functions to acquire/release the ctl, prof, and
rtree mutexes. This fixes various fork() child process deadlocks, but
one possible deadlock remains (intentionally) unaddressed: prof
backtracing can acquire runtime library mutexes, so deadlock is still
possible if heap profiling is enabled during fork(). This deadlock is
known to be a real issue in at least the case of libgcc-based
backtracing.
Reported by tfengjun.
