[pypy-commit] pypy.org extradoc: Document the recently discovered low-memory-usage command-line.

[arigo]

Author: Armin Rigo <arigo at tunes.org>
Branch: extradoc
Changeset: r231:73c1c9cb6e05
Date: 2011-08-18 17:00 +0200
http://bitbucket.org/pypy/pypy.org/changeset/73c1c9cb6e05/

Log:	Document the recently discovered low-memory-usage command-line.

diff --git a/source/download.txt b/source/download.txt
--- a/source/download.txt
+++ b/source/download.txt
@@ -128,17 +128,24 @@
      pypy translate.py -Ojit --backend=cli  # only for branch/cli-jit
 
 5. Enjoy Mandelbrot ``:-)``  It takes on the order of half an hour to
-   finish the translation, and 2 GB of RAM on a 32-bit system
-   and 4 GB on 64-bit systems.  (Do not start a translation on a
-   machine with insufficient RAM!  It will just swap forever.)
+   finish the translation, and 2.x GB of RAM on a 32-bit system
+   and 4.x GB on 64-bit systems.  (Do not start a translation on a
+   machine with insufficient RAM!  It will just swap forever.  See
+   notes below in that case.)
 
 Notes:
 
 * It is recommended to use PyPy to do translations, instead of using CPython,
-  because it is twice as fast.  (Using CPython would lower the memory
-  requirement down to 1.2 GB on 32-bit, 2.4 GB on 64-bit.)
-  You should just start by downloading an official release of PyPy (with the
-  JIT).
+  because it is twice as fast.  You should just start by downloading an
+  official release of PyPy (with the JIT).
+
+* If RAM usage is a problem, then you can (for now) tweak some parameters
+  via environment variables and command-line options.  The following command
+  takes a bit more time, but finishes with only using 3.0 GB of RAM (on
+  Linux 64-bit; probably not much more than 1.5 GB on 32-bit).  It should be
+  noted that it is less than with CPython. ::
+
+    PYPY_GC_MAX_DELTA=200MB pypy --jit loop_longevity=300 ./translate.py -Ojit
 
 * Because of ``asmgcroot``, compiling the generated C files containing the JIT
   is delicate.  It requires using either MSVC or gcc with no particularly