Add a statistic for tracking how many cells are marked conservatively.

This allows an informed choice for deciding how many segments to
create.  After startup, ~2% of the cells are scanned conservatively.

libguile/gc-mark.c

@@ -78,7 +78,7 @@ scm_mark_all (void)
   scm_i_init_guardians_for_gc ();
   
   scm_i_clear_mark_space ();
-  
+  scm_i_find_heap_calls = 0;
   /* Mark every thread's stack and registers */
   scm_threads_mark_stacks ();
 
@@ -404,7 +404,7 @@ scm_gc_mark_dependencies (SCM p)
       {
     /* We are in debug mode.  Check the ptr exhaustively. */
 	
-	valid_cell = valid_cell && (scm_i_find_heap_segment_containing_object (ptr) >= 0);
+	valid_cell = valid_cell && scm_in_heap_p (ptr);
       }
     
 #endif

libguile/gc-segment-table.c

@@ -115,12 +115,14 @@ scm_i_insert_segment (scm_t_heap_segment *seg)
 
   I think this function is too long to be inlined. --hwn
 */
+
 int
 scm_i_find_heap_segment_containing_object (SCM obj)
 {
   if (!CELL_P (obj))
     return -1;
 
+  scm_i_find_heap_calls ++;
   if ((scm_t_cell *) obj < lowest_cell || (scm_t_cell *) obj >= highest_cell)
     return -1;
   

libguile/gc-segment.c

@@ -44,6 +44,7 @@ scm_i_get_new_heap_segment (scm_t_cell_type_statistics *freelist,
   if (len < SCM_MIN_HEAP_SEG_SIZE)
     len = SCM_MIN_HEAP_SEG_SIZE;
 
+  /* todo: consider having a more flexible lower bound. */
   {
     scm_t_heap_segment *seg = scm_i_make_empty_heap_segment (freelist);
 

libguile/gc.c

@@ -210,7 +210,7 @@ unsigned long scm_mtrigger;
 unsigned long scm_cells_allocated = 0;
 unsigned long scm_last_cells_allocated = 0;
 unsigned long scm_mallocated = 0;
-
+long int scm_i_find_heap_calls = 0;
 /* Global GC sweep statistics since the last full GC.  */
 scm_t_sweep_statistics scm_i_gc_sweep_stats = { 0, 0 };
 
@@ -241,6 +241,7 @@ SCM_SYMBOL (sym_gc_time_taken, "gc-time-taken");
 SCM_SYMBOL (sym_gc_mark_time_taken, "gc-mark-time-taken");
 SCM_SYMBOL (sym_times, "gc-times");
 SCM_SYMBOL (sym_cells_marked, "cells-marked");
+SCM_SYMBOL (sym_cells_marked_conservatively, "cells-marked-conservatively");
 SCM_SYMBOL (sym_cells_swept, "cells-swept");
 SCM_SYMBOL (sym_malloc_yield, "malloc-yield");
 SCM_SYMBOL (sym_cell_yield, "cell-yield");
@@ -314,6 +315,7 @@ SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
   unsigned long int local_scm_gc_times;
   unsigned long int local_scm_gc_mark_time_taken;
   unsigned long int local_protected_obj_count;
+  unsigned long int local_conservative_scan_count;
   double local_scm_gc_cells_swept;
   double local_scm_gc_cells_marked;
   double local_scm_total_cells_allocated;
@@ -327,6 +329,7 @@ SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
   /* Below, we cons to produce the resulting list.  We want a snapshot of
    * the heap situation before consing.
    */
+  local_conservative_scan_count = scm_i_find_heap_calls;
   local_scm_mtrigger = scm_mtrigger;
   local_scm_mallocated = scm_mallocated;
   local_scm_heap_size =
@@ -369,6 +372,8 @@ SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
 			  scm_from_double (local_scm_total_cells_allocated)),
 		scm_cons (sym_heap_size,
 			  scm_from_ulong (local_scm_heap_size)),
+		scm_cons (sym_cells_marked_conservatively,
+			  scm_from_ulong (local_conservative_scan_count)),
 		scm_cons (sym_mallocated,
 			  scm_from_ulong (local_scm_mallocated)),
 		scm_cons (sym_mtrigger,

libguile/private-gc.h

@@ -275,6 +275,7 @@ SCM_INTERNAL SCM scm_i_all_segments_statistics (SCM hashtab);
 SCM_INTERNAL unsigned long *scm_i_segment_table_info(int *size);
 
 extern long int scm_i_deprecated_memory_return;
+extern long int scm_i_find_heap_calls;
 
 /*
   global init funcs.