[PATCH 1/1] Prevent excessive major gcs by preserving a decent amount of unused heap

[Evan Hanson]

From: megane <address@hidden>

Signed-off-by: Evan Hanson <address@hidden>
---
 manual/Using the compiler |  2 ++
 runtime.c                 | 11 +++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git manual/Using the compiler manual/Using the compiler
index fd656362..7a96920a 100644
--- manual/Using the compiler   
+++ manual/Using the compiler   
@@ -223,6 +223,8 @@ by the startup code and will not be contained in the result 
of
 
 ; {{-:hmNUMBER}} : Specifies a maximal heap size (including both semispaces). 
The default is (2GB - 15).
 
+; {{-:hfNUMBER}} : Specifies the minimum avilable heap space. If the free 
space (in one semispace) is less than this number (4MB by default), then the 
heap is grown.
+
 ; {{-:hsPERCENTAGE}} : Sets the shrink rate of the heap in percent. The heap 
is shrunk to {{PERCENTAGE}} when the watermark is reached. The default is 50.  
Note: If you want to make sure that the heap never shrinks, specify a value of 
{{0}}.  (this can be useful in situations where an optimal heap-size is known 
in advance). 
 
 ; {{-:huPERCENTAGE}} : Sets the memory usage watermark below which heap 
shrinking is triggered. The default is 25.
diff --git runtime.c runtime.c
index 8e049623..b285b4f2 100644
--- runtime.c
+++ runtime.c
@@ -163,6 +163,7 @@ static C_TLS int timezone;
 #define DEFAULT_HEAP_GROWTH            200
 #define DEFAULT_HEAP_SHRINKAGE         50
 #define DEFAULT_HEAP_SHRINKAGE_USED    25
+#define DEFAULT_HEAP_MIN_FREE          (4 * 1024 * 1024)
 #define DEFAULT_FORWARDING_TABLE_SIZE  32
 #define DEFAULT_LOCATIVE_TABLE_SIZE    32
 #define DEFAULT_COLLECTIBLES_SIZE      1024
@@ -360,6 +361,7 @@ C_TLS C_uword
   C_heap_growth = DEFAULT_HEAP_GROWTH,
   C_heap_shrinkage = DEFAULT_HEAP_SHRINKAGE,
   C_heap_shrinkage_used = DEFAULT_HEAP_SHRINKAGE_USED,
+  C_heap_min_free = DEFAULT_HEAP_MIN_FREE,
   C_maximal_heap_size = DEFAULT_MAXIMAL_HEAP_SIZE;
 C_TLS time_t
   C_startup_time_seconds,
@@ -1362,6 +1364,7 @@ void CHICKEN_parse_command_line(int argc, char *argv[], 
C_word *heap, C_word *st
                 " -:o              disable stack overflow checks\n"
                 " -:hiSIZE         set initial heap size\n"
                 " -:hmSIZE         set maximal heap size\n"
+                 " -:hfSIZE         set minimum unused heap size\n"
                 " -:hgPERCENTAGE   set heap growth percentage\n"
                 " -:hsPERCENTAGE   set heap shrink percentage\n"
                 " -:huPERCENTAGE   set percentage of memory used at which heap 
will be shrunk\n"
@@ -1390,6 +1393,9 @@ void CHICKEN_parse_command_line(int argc, char *argv[], 
C_word *heap, C_word *st
            *heap = arg_val(ptr + 1); 
            heap_size_changed = 1;
            goto next;
+          case 'f':
+           C_heap_min_free = arg_val(ptr + 1);
+           goto next;
          case 'g':
            C_heap_growth = arg_val(ptr + 1);
            goto next;
@@ -3605,7 +3611,7 @@ C_regparm void C_fcall C_reclaim(void *trampoline, C_word 
c)
     /*** isn't gc_mode always GC_MAJOR here? */
     /* NOTE: count is actual usage, heap_size is both halves */
     if(gc_mode == GC_MAJOR && 
-       count < percentage(heap_size/2, C_heap_shrinkage_used) &&
+       C_heap_min_free + count < percentage(heap_size / 2, 
C_heap_shrinkage_used) &&
        C_heap_shrinkage > 0 && 
        heap_size > MINIMAL_HEAP_SIZE && !C_heap_size_is_fixed)
       C_rereclaim2(percentage(heap_size, C_heap_shrinkage), 0);
@@ -3809,7 +3815,8 @@ C_regparm void C_fcall really_mark(C_word *x)
     n = C_header_size(p);
     bytes = (h & C_BYTEBLOCK_BIT) ? n : n * sizeof(C_word);
 
-    if(((C_byte *)p2 + bytes + sizeof(C_word)) > tospace_limit) {
+    /* Check for needed size plus minimum unused block: */
+    if(((C_byte *)p2 + bytes + sizeof(C_word) + C_heap_min_free) > 
tospace_limit) {
       /* Detect impossibilities before GC_REALLOC to preserve state: */
       if (C_in_stackp((C_word)p) && bytes > stack_size)
         panic(C_text("Detected corrupted data in stack"));
-- 
2.25.1