- Document the new ZEND_DONT_UNLOAD_MODULES environment variable.

Zend/README.ZEND_MM

@@ -9,7 +9,7 @@ allocation overhead and speedup memory management.
 
 The new manager's "configure" has no "--disable-zend-memory-manager" option,
 but it has "--enable-malloc-mm" instead.  It is enabled by default in DEBUG
-build and disabled by default in RELEASE build.  when enabled it allows selecting
+build and disabled by default in RELEASE build. When enabled it allows selecting
 between malloc and emalloc at runtime so you can use internal and external memory
 debuggers without recompilation.
 
@@ -24,6 +24,15 @@ Zend MM disabled:
 
     $ USE_ZEND_ALLOC=0 valgrind --leak-check=full sapi/cli/php -r 'leak();'
 
+Shared extensions:
+------------------
+
+Since PHP 5.4 it is possible to prevent shared extensions from unloading so
+that valgrind can correctly track the memory leaks in shared extensions. For
+this there is the ZEND_DONT_UNLOAD_MODULES environment variable. If set, then
+DL_UNLOAD() is skipped during the shutdown of shared extensions.
+
+
 Tweaking:
 ---------