diff --git a/ChangeLog b/ChangeLog
index 7768913..78ec5ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Release x.x.x - 2020/04/03
+- jemalloc v5.2.1
+
+Release x.x.x - 2016/08/18
+- jemalloc v4.2.1
+
+Release x.x.x - 2015/12/03
+- jemalloc v4.0.4
+
 Release 1.0.1 - 2015/01/15
 - just exec without spawn
 
diff --git a/Gemfile b/Gemfile
index 851fabc..cd8aa9e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,2 +1,3 @@
 source 'https://rubygems.org'
-gemspec
+
+gemspec
\ No newline at end of file
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..6e2729b
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2020 GarazLab https://garazlab.com
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
index 156c6f9..71b98ad 100644
--- a/README.md
+++ b/README.md
@@ -2,11 +2,16 @@
 
 Instant [jemalloc](http://www.canonware.com/jemalloc/) injection into Ruby apps, for better performance and less memory.
 
+# Example
+
+[GarazLab](https://garazlab.com) uses this gem with its below rails applications for its internal memory allocation:
+1. [Ruby on Rails Page Builder](https://garazlab.com/product/ruby-on-rails-page-builder)
+
 # Why jemalloc?
 
-Ruby relies on malloc(3) for its internal memory allocation. Using better malloc() implementation will boost your application performance, and supress the memory usage.
+Ruby relies on malloc(3) for its internal memory allocation. Using a better malloc() implementation will boost your application's performance, and reduce it's memory usage.
 
-jemalloc is a malloc(3) implementation, originally developed by Jason Evans. jemalloc handles small object better than other allocators so usually gives better performance and memory usage to Ruby programs.
+jemalloc is a malloc(3) implementation, originally developed by Jason Evans. jemalloc handles small objects better than other allocators, so it usually gives better performance and memory usage to Ruby programs.
 
 # Why jemalloc?
 
@@ -14,7 +19,7 @@ Installing jemalloc separately from Ruby is pain in some cases (e.g. Heroku, Eng
 
 # Install
 
-Install `jemalloc` gem in your application. For [bundler](http://gembundler.com/) based application, please add the following line into your Gemfile, and and install `jemalloc` by `bundle install`.
+Install `jemalloc` gem in your application. For [bundler](http://gembundler.com/) based applications, please add the following line into your Gemfile, and and install `jemalloc` by `bundle install`.
 
     gem 'jemalloc'
 
@@ -31,6 +36,14 @@ Execute your application with `je` command, which is contained in `je` gem. Exam
     => Booting WEBrick
     ...
 
+# Advanced: Valgrind
+
+Jemalloc is built to use [Valgrind](http://valgrind.org/) by default. As Valgrind is not installed on Mac systems or on Heroku, this gem disables Valgrind by using `--disable-valgrind` during the configure process.
+
+You can enable Valgrind by specifying: `bundle config build.jemalloc --with-valgrind` before installing jemalloc-rb using Bundler.
+
+Please note, if you want to enable Valgrind for all projects which use Bundler, you need to use the `--global` flag, e.g. `bundle config --global build.jemalloc --with-valgrind`
+
 # Limitation
 
 Currently, this gem works only on Linux and Mac OS X.
diff --git a/ext/jemalloc/extconf.rb b/ext/jemalloc/extconf.rb
index 010da49..6a04e11 100644
--- a/ext/jemalloc/extconf.rb
+++ b/ext/jemalloc/extconf.rb
@@ -2,7 +2,7 @@
 require 'rbconfig'
 
 $stdout.sync = true
-pkg = "jemalloc-3.4.0"
+pkg = "jemalloc-5.2.1"
 
 def sys(cmd)
   puts "$ #{cmd}"
@@ -12,22 +12,32 @@ def sys(cmd)
   ret
 end
 
+# grab config options
+config_options = []
+config_options << '--disable-valgrind' unless (with_config('valgrind') == false)
+
 # monfigure and copy sources to cur_dir
 src_dir = File.expand_path(File.dirname(__FILE__))
 cur_dir = Dir.pwd
 Dir.chdir File.dirname(__FILE__) do
   # cleanup
-  FileUtils.remove_dir(pkg, force = true)
+  FileUtils.remove_dir(pkg, true)
 
   # decompress and copy source files
   sys "tar vjxf #{pkg}.tar.bz2"
   Dir.chdir(pkg) do
     # configure
-    sys "./configure"
+    sys "./configure #{ config_options.join(' ') }"
     # zone.c is only for Mac OS X
     if RbConfig::CONFIG['target_vendor'] != "apple"
       sys "rm -fR src/zone.c"
     end
+    # if we don't remove this explicitly, mkmf will try to include it
+    # and that causes issues when '--disable-valgrind' is used
+    # le sigh
+    unless with_config('valgrind') == false
+      sys "rm -fR src/valgrind.c"
+    end
     # mkmf only allows *.c files on current dir
     sys "cp src/*.c #{src_dir}"
   end
diff --git a/ext/jemalloc/jemalloc-3.4.0.tar.bz2 b/ext/jemalloc/jemalloc-3.4.0.tar.bz2
deleted file mode 100644
index 7ee12e7..0000000
Binary files a/ext/jemalloc/jemalloc-3.4.0.tar.bz2 and /dev/null differ
diff --git a/ext/jemalloc/jemalloc-5.2.1.tar.bz2 b/ext/jemalloc/jemalloc-5.2.1.tar.bz2
new file mode 100644
index 0000000..75baa3f
Binary files /dev/null and b/ext/jemalloc/jemalloc-5.2.1.tar.bz2 differ
diff --git a/lib/jemalloc/version.rb b/lib/jemalloc/version.rb
index 0a33c05..69a53e7 100644
--- a/lib/jemalloc/version.rb
+++ b/lib/jemalloc/version.rb
@@ -1,3 +1,3 @@
 module JEMalloc
-  VERSION = "1.0.1"
+  VERSION = "1.5.2"
 end