[m-rev.] for review: add --boehm-gc-free-space-divisor option

[Peter Wang]

Branches: main

Add `--boehm-gc-free-space-divisor <n>' option for MERCURY_OPTIONS.
This sets the value of a tunable parameter in Boehm GC to trade off heap
size for collection time.

runtime/mercury_wrapper.c:
	Add the option.

doc/user_guide.texi:
	Add documentation.

scripts/mdprof.in:
	Add some sample code to enable the option when calling the deep
	profiler CGI program.

diff --git a/doc/user_guide.texi b/doc/user_guide.texi
index d4a749c..8a78c79 100644
--- a/doc/user_guide.texi
+++ b/doc/user_guide.texi
@@ -9834,6 +9834,14 @@ garbage collector, and requires @samp{--enable-gc-munmap} to be passed to
 @samp{configure}. (This may not work with all platforms).
 
 @sp 1
+ at item --boehm-gc-free-space-divisor=@var{N}
+ at findex --boehm-gc-free-space-divisor=@var{N}
+This option sets the value of the free space divisor in the Boehm garbage
+collector to @var{N}. The default value is 3. Increasing its value will reduce
+heap space but increase collection time.
+See the Boehm GC documentation for details.
+
+ at sp 1
 @item --boehm-gc-calc-time
 @findex --boehm-gc-calc-time
 This option enables code in the Boehm garbage collector to calculate
diff --git a/runtime/mercury_wrapper.c b/runtime/mercury_wrapper.c
index 912e731..5a4de9d 100644
--- a/runtime/mercury_wrapper.c
+++ b/runtime/mercury_wrapper.c
@@ -1214,6 +1214,7 @@ enum MR_long_option {
     MR_TRACE_COUNT_FILE,
     MR_MEM_USAGE_REPORT,
     MR_BOEHM_GC_MUNMAP,
+    MR_BOEHM_GC_FREE_SPACE_DIVISOR,
     MR_BOEHM_GC_CALC_TIME
 };
 
@@ -1314,6 +1315,7 @@ struct MR_option MR_long_opts[] = {
     { "trace-count-summary-max",        1, 0, MR_TRACE_COUNT_SUMMARY_MAX_OPT },
     { "mem-usage-report",               1, 0, MR_MEM_USAGE_REPORT },
     { "boehm-gc-munmap",                0, 0, MR_BOEHM_GC_MUNMAP },
+    { "boehm-gc-free-space-divisor",    1, 0, MR_BOEHM_GC_FREE_SPACE_DIVISOR },
     { "boehm-gc-calc-time",             0, 0, MR_BOEHM_GC_CALC_TIME },
 
     /* This needs to be kept at the end. */
@@ -1845,6 +1847,20 @@ MR_process_options(int argc, char **argv)
 #endif
                 break;
 
+            case MR_BOEHM_GC_FREE_SPACE_DIVISOR:
+                if (sscanf(MR_optarg, "%lu", &size) != 1) {
+                    MR_usage();
+                }
+
+                if (size < 1) {
+                    MR_usage();
+                }
+
+#ifdef MR_BOEHM_GC
+                GC_set_free_space_divisor(size);
+#endif
+                break;
+
             case MR_BOEHM_GC_CALC_TIME:
 #ifdef MR_BOEHM_GC
                 GC_mercury_calc_gc_time = MR_TRUE;
diff --git a/scripts/mdprof.in b/scripts/mdprof.in
index 6b16ce5..5d2462c 100644
--- a/scripts/mdprof.in
+++ b/scripts/mdprof.in
@@ -17,4 +17,14 @@
 
 PATH=@prefix@/bin:$PATH
 export PATH
+
+# Use less heap at the expense of increased time spent in the GC.
+# The value is "experimentally determined" (guessed).
+if false
+then
+    MERCURY_OPTIONS_mdprof_cgi="--boehm-gc-free-space-divisor 10 \
+	${MERCURY_OPTIONS_mdprof_cgi}"
+    export MERCURY_OPTIONS_mdprof_cgi
+fi
+
 exec mdprof_cgi



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