jemalloc: build with profiling support

CMakeLists.txt

@@ -149,7 +149,7 @@ ExternalProject_Add(libjemalloc
                     SOURCE_DIR ${CMAKE_SOURCE_DIR}/build_deps/jemalloc
                     DEPENDS gitsubmodules
                     UPDATE_COMMAND autoconf
-                    CONFIGURE_COMMAND ${CMAKE_SOURCE_DIR}/build_deps/jemalloc/configure --prefix=${CMAKE_BINARY_DIR}/jemalloc --enable-autogen --enable-prof-libunwind
+                    CONFIGURE_COMMAND ${CMAKE_SOURCE_DIR}/build_deps/jemalloc/configure --prefix=${CMAKE_BINARY_DIR}/jemalloc --enable-autogen --enable-prof --enable-prof-libunwind
                     BUILD_COMMAND ${MAKE_PRG}
                     INSTALL_COMMAND ${MAKE_PRG} install_bin install_lib
                     LOG_UPDATE ON

docs/MEMORY_PROFILING.md

+There are different ways to do heap profiling but it looks like jemalloc heap profiling works currently best for Pyston. (unfortunately valgrind often crashes currently if the ICs are enabled)
+
+## Prerequisites
+Pyston comes with jemalloc which is already configured with enabled profiling.
+But because we currently don't install the header one needs to run as a workaround `sudo apt-get install libjemalloc-dev` to install the system package and rebuild jemalloc afterwards.
+
+## Usage
+The jemalloc documentation about profiling can be found [here](https://github.com/jemalloc/jemalloc/wiki/Use-Case%3A-Heap-Profiling) and the one about leak checking [here](https://github.com/jemalloc/jemalloc/wiki/Use-Case%3A-Leak-Checking).
+
+an example usage is:
+```
+~/pyston$ MALLOC_CONF="prof:true,prof_prefix:jeprof.out" ./pyston_release minibenchmarks/raytrace.py
+~/pyston$ build_deps/jemalloc/bin/pprof pyston_release jeprof.out.*
+(pprof) top3
+Total: 4.5 MB
+     1.0  22.2%  22.2%      1.0  22.2% pyston::BST_FunctionDef::operator new (inline)
+     0.5  11.1%  33.3%      0.5  11.1% pyston::DenseMap::allocateBuckets (inline)
+     0.5  11.1%  44.5%      0.5  11.1% pyston::CFG::addBlock
+```
+