From 2ef0e22c550092d62a21db01fc40cf151e1a2dfc Mon Sep 17 00:00:00 2001
From: Gareth Rees <gdr@ravenbrook.com>
Date: Fri, 11 Apr 2014 21:15:09 +0100
Subject: [PATCH] Default value for mps_key_arena_size makes it easier to
 create arenas.

Copied from Perforce
 Change: 185472
 ServerID: perforce.ravenbrook.com
---
 mps/code/arenavm.c                |  6 +++---
 mps/code/config.h                 |  2 ++
 mps/manual/source/topic/arena.rst | 31 ++++++++++++++++---------------
 3 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/mps/code/arenavm.c b/mps/code/arenavm.c
index 15b79bbed51..81e0684c436 100644
--- a/mps/code/arenavm.c
+++ b/mps/code/arenavm.c
@@ -480,7 +480,7 @@ ARG_DEFINE_KEY(arena_contracted, Fun);
 
 static Res VMArenaInit(Arena *arenaReturn, ArenaClass class, ArgList args)
 {
-  Size userSize;        /* size requested by user */
+  Size userSize = VM_ARENA_SIZE_DEFAULT; /* size requested by user */
   Size chunkSize;       /* size actually created */
   Size vmArenaSize; /* aligned size of VMArenaStruct */
   Res res;
@@ -495,8 +495,8 @@ static Res VMArenaInit(Arena *arenaReturn, ArenaClass class, ArgList args)
   AVER(class == VMArenaClassGet());
   AVERT(ArgList, args);
 
-  ArgRequire(&arg, args, MPS_KEY_ARENA_SIZE);
-  userSize = arg.val.size;
+  if (ArgPick(&arg, args, MPS_KEY_ARENA_SIZE))
+    userSize = arg.val.size;
 
   AVER(userSize > 0);
   
diff --git a/mps/code/config.h b/mps/code/config.h
index b781f1da591..0afa66c06bb 100644
--- a/mps/code/config.h
+++ b/mps/code/config.h
@@ -366,6 +366,8 @@
    pool to be very heavily used. */
 #define CONTROL_EXTEND_BY 4096
 
+#define VM_ARENA_SIZE_DEFAULT ((Size)1 << 20)
+
 
 /* Stack configuration */
 
diff --git a/mps/manual/source/topic/arena.rst b/mps/manual/source/topic/arena.rst
index 5220ece4007..1925117cc84 100644
--- a/mps/manual/source/topic/arena.rst
+++ b/mps/manual/source/topic/arena.rst
@@ -233,18 +233,18 @@ Virtual memory arenas
     more efficient.
 
     When creating a virtual memory arena, :c:func:`mps_arena_create_k`
-    requires one :term:`keyword argument`:
+    accepts one :term:`keyword argument` on all platforms:
 
-    * :c:macro:`MPS_KEY_ARENA_SIZE` (type :c:type:`size_t`). is the
-      initial amount of virtual address space, in :term:`bytes (1)`,
-      that the arena will reserve (this space is initially reserved so
-      that the arena can subsequently use it without interference from
-      other parts of the program, but most of it is not committed, so
-      it doesn't require any RAM or backing store). The arena may
-      allocate more virtual address space beyond this initial
-      reservation as and when it deems it necessary. The MPS is most
-      efficient if you reserve an address space that is several times
-      larger than your peak memory usage.
+    * :c:macro:`MPS_KEY_ARENA_SIZE` (type :c:type:`size_t`, default
+      2\ :superscript:`20`) is the initial amount of virtual address
+      space, in :term:`bytes (1)`, that the arena will reserve (this
+      space is initially reserved so that the arena can subsequently
+      use it without interference from other parts of the program, but
+      most of it is not committed, so it doesn't require any RAM or
+      backing store). The arena may allocate more virtual address
+      space beyond this initial reservation as and when it deems it
+      necessary. The MPS is most efficient if you reserve an address
+      space that is several times larger than your peak memory usage.
 
       .. note::
 
@@ -252,8 +252,8 @@ Virtual memory arenas
           more times it has to extend its address space, the less
           efficient garbage collection will become.
 
-    An optional :term:`keyword argument` may be passed, but is
-    only used on the Windows operating system:
+    A second optional :term:`keyword argument` may be passed, but it
+    only has any effect on the Windows operating system:
 
     * :c:macro:`MPS_KEY_VMW3_TOP_DOWN` (type :c:type:`mps_bool_t`). If
       true, the arena will allocate address space starting at the
@@ -273,8 +273,9 @@ Virtual memory arenas
 
     If the MPS fails to allocate memory for the internal arena
     structures, :c:func:`mps_arena_create_k` returns
-    :c:macro:`MPS_RES_MEMORY`. Either ``size`` was far too small or
-    the operating system refused to provide enough memory.
+    :c:macro:`MPS_RES_MEMORY`. Either :c:macro:`MPS_KEY_ARENA_SIZE`
+    was far too small or the operating system refused to provide
+    enough memory.
 
     For example::