From d9ac33720c2d5e1c35b0282292f8f1a61c123ddf Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 18 Mar 2020 22:24:19 -0700
Subject: gc: small memory support.

* configure (small_mem): New variable.  Provide help text and
show default value of --small-mem option.  Generate
CONFIG_SMALL_MEM in config.h.

* gc.c (HEAP_SIZE, CHECKOBJ_VEC_SIZE, MUTOBJ_VEC_SIZE,
FULL_GC_INTERVAL, FRESHOBJ_VEC_SIZE, DFL_MALLOC_DELTA_THRESH):
Define conservative values of these constants if
CONFIG_SMALL_MEM is in effect.
---
 configure | 10 ++++++++++
 gc.c      | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/configure b/configure
index fad3da0c..a32f5306 100755
--- a/configure
+++ b/configure
@@ -149,6 +149,7 @@ lit_align=
 extra_debugging=
 debug_support=y
 gen_gc=y
+small_mem=
 have_dbl_decimal_dig=
 have_unistd=
 have_sys_stat=
@@ -484,6 +485,14 @@ gen-gc [$gen_gc]
   When disabled, the garbage collector performs a full object traversal and
   sweep on each garbage collection.
 
+small-mem [$small_mem]
+
+  Use --small-mem to make the memory management use less memory,
+  for embedded systems with less RAM, at the possible cost of some
+  run-time penalty. Objects are allocated in smaller blocks,
+  and certain global book-keeping arrays in the generational garbage
+  collector are smaller, resulting in more frequent collections.
+
 !
   exit 1
 fi
@@ -3545,6 +3554,7 @@ $make conftest.clean
 
 [ -n "$debug_support" ] && printf "#define CONFIG_DEBUG_SUPPORT 1\n" >> config.h
 [ -n "$gen_gc" ] && printf "#define CONFIG_GEN_GC 1\n" >> config.h
+[ "$small_mem" ] && printf "#define CONFIG_SMALL_MEM 1\n" >> config.h
 
 #
 # Regenerate config.make
diff --git a/gc.c b/gc.c
index f3a354c6..df9de0fb 100644
--- a/gc.c
+++ b/gc.c
@@ -46,12 +46,22 @@
 #include "unwind.h"
 
 #define PROT_STACK_SIZE         1024
+
+#if CONFIG_SMALL_MEM
+#define HEAP_SIZE               4096
+#define CHECKOBJ_VEC_SIZE       HEAP_SIZE
+#define MUTOBJ_VEC_SIZE         HEAP_SIZE
+#define FULL_GC_INTERVAL        20
+#define FRESHOBJ_VEC_SIZE       (2 * HEAP_SIZE)
+#define DFL_MALLOC_DELTA_THRESH (16L * 1024 * 1024)
+#else
 #define HEAP_SIZE               16384
 #define CHECKOBJ_VEC_SIZE       (2 * HEAP_SIZE)
 #define MUTOBJ_VEC_SIZE         (2 * HEAP_SIZE)
 #define FULL_GC_INTERVAL        40
 #define FRESHOBJ_VEC_SIZE       (8 * HEAP_SIZE)
 #define DFL_MALLOC_DELTA_THRESH (64L * 1024 * 1024)
+#endif
 
 #if HAVE_MEMALIGN || HAVE_POSIX_MEMALIGN
 #define OBJ_ALIGN (sizeof (obj_t))
-- 
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