add PLT_INCREMENTAL_GC

Although calling `(collect-garbage 'incremental)` in a program with
a periodic task is the best way to request incremental collection, it's
handy for some experiments to have an environment variable that turns
it on permanently.

This change also makes incremental-mode minor collections log as "mIn"
instead of "min", and it changes the first field of the logged
`gc-info` structure to be a mode symbol instead of a boolean.

pkgs/racket-doc/scribblings/reference/memory.scrbl

@@ -199,7 +199,11 @@ execution. Otherwise, @racket[#f] is returned.}
 @section[#:tag "garbagecollection"]{Garbage Collection}
 
 Set the @as-index{@envvar{PLTDISABLEGC}} environment variable (to any
-value) before Racket starts to disable @tech{garbage collection}.
+value) before Racket starts to disable @tech{garbage collection}. Set
+the @as-index{@envvar{PLT_INCREMENTAL_GC}} environment variable to
+request incremental mode at all times, but calling
+@racket[(collect-garbage 'incremental)] in a program with a periodic
+task is generally a better mechanism for requesting incremental mode.
 
 In Racket 3m (the main variant of Racket), each garbage collection
 logs a message (see @secref["logging"]) at the @racket['debug] level with topic @racket['GC].
@@ -209,18 +213,28 @@ versions of Racket may use a @racket[gc-info] @tech{prefab} structure
 with additional fields:
 
 @racketblock[
-(struct gc-info (major? pre-amount pre-admin-amount code-amount
+(struct gc-info (mode pre-amount pre-admin-amount code-amount
-                        post-amount post-admin-amount
+                      post-amount post-admin-amount
-                        start-process-time end-process-time
+                      start-process-time end-process-time
-                        start-time end-time)
+                      start-time end-time)
   #:prefab)
 ]
 
 @itemlist[
 
- @item{The @racket[major?] field indicates whether the collection was
+ @item{The @racket[mode] field is a symbol @racket['major],
-       a ``major'' collection that inspects all memory or a ``minor''
+       @racket['minor], or @racket['incremental]; @racket['major]
-       collection that mostly inspects just recent allocations.}
+       indicates a collection that inspects all memory,
+       @racket['minor] indicates collection that mostly inspects just
+       recent allocations, and @racket['incremental] indicates a minor
+       collection that performs extra work toward the next major
+       collection.
+
+       @history[#:changed "6.3.0.7" @elem{Changed first field from a
+                                          boolean (@racket[#t] for
+                                          @racket['major], @racket[#f]
+                                          for @racket['minor]) to a
+                                          mode symbol.}]}
 
  @item{The @racket[pre-amount] field reports place-local memory use
       (i.e., not counting the memory use of child places) in bytes at
@@ -286,6 +300,7 @@ collection mode, the text has the format
               @elem{Processor time since startup of garbage collection's start}))
 ]}
 
+@history[#:changed "6.3.0.7" @elem{Added @envvar{PLT_INCREMENTAL_GC}.}]
 
 @defproc[(collect-garbage [request (or/c 'major 'minor 'incremental) 'major]) void?]{
 
@@ -314,7 +329,8 @@ garbage-collection mode, depending on @racket[request]:
        major collections any sooner than they would occur otherwise.}
 
  @item{@racket['incremental] --- Requests that each minor
-       collection performs incremental work toward a major collection.
+       collection performs incremental work toward a major collection
+       (but does not request an immediate minor collection).
        This incremental-mode request expires at the next major
        collection.
 

racket/src/racket/cmdline.inc

@@ -1542,6 +1542,9 @@ static int run_from_cmd_line(int argc, char *_argv[],
   if (getenv("PLTDISABLEGC")) {
     scheme_enable_garbage_collection(0);
   }
+  if (getenv("PLT_INCREMENTAL_GC")) {
+    scheme_incremental_garbage_collection(1);
+  }
 #endif
 
   scheme_set_logging_spec(syslog_level, stderr_level);

racket/src/racket/gc2/gc2.h

@@ -31,7 +31,7 @@ typedef int (*Fixup_Proc)(void *obj);
 typedef int (*Fixup2_Proc)(void *obj, struct NewGC *);
 typedef void (*GC_collect_start_callback_Proc)(void);
 typedef void (*GC_collect_end_callback_Proc)(void);
-typedef void (*GC_collect_inform_callback_Proc)(int master_gc, int major_gc, 
+typedef void (*GC_collect_inform_callback_Proc)(int master_gc, int major_gc, int inc_gc,
                                                 intptr_t pre_used, intptr_t post_used,
                                                 intptr_t pre_admin, intptr_t post_admin,
                                                 intptr_t post_child_places_used);
@@ -174,6 +174,10 @@ GC2_EXTERN void GC_request_incremental_mode(void);
 /*
    Requests incremental mode; lasts until the next major collection. */
   
+GC2_EXTERN void GC_set_incremental_mode(int on);
+/*
+   Sets whether incremental mode is the default. */
+  
 GC2_EXTERN void GC_free_all(void);
 /*
    Releases all memory, removes all signal handlers, etc.

racket/src/racket/gc2/newgc.c

@@ -252,7 +252,7 @@ MAYBE_UNUSED static void GCVERBOSEprintf(NewGC *gc, const char *fmt, ...) {
 #define AGE_GEN_0_TO_GEN_HALF(gc) ((gc)->memory_in_use > (GEN0_MAX_SIZE * 8))
 
 /* Incremental mode */
-#define ALWAYS_COLLECT_INCREMENTAL_ON_MINOR 0
+static int always_collect_incremental_on_minor = 0;
 #define INCREMENTAL_COLLECT_FUEL_PER_100M (24 * 1024)
 #define INCREMENTAL_REPAIR_FUEL_PER_100M  512
 
@@ -3558,6 +3558,11 @@ void GC_request_incremental_mode(void)
   gc->incremental_requested = 1;
 }
 
+void GC_set_incremental_mode(int on)
+{
+  always_collect_incremental_on_minor = 1;
+}
+
 void GC_enable_collection(int on)
 {
   NewGC *gc = GC_get_GC();
@@ -5847,7 +5852,7 @@ static void garbage_collect(NewGC *gc, int force_full, int no_full, int switchin
   gc->need_fixup = 0;
 
   do_incremental = (!gc->gc_full && (gc->incremental_requested
-                                     || ALWAYS_COLLECT_INCREMENTAL_ON_MINOR));
+                                     || always_collect_incremental_on_minor));
   if (!postmaster_and_place_gc(gc))
     do_incremental = 0;
   
@@ -6053,7 +6058,7 @@ static void garbage_collect(NewGC *gc, int force_full, int no_full, int switchin
     is_master = (gc == MASTERGC);
 #endif
     park_for_inform_callback(gc);
-    gc->GC_collect_inform_callback(is_master, gc->gc_full, 
+    gc->GC_collect_inform_callback(is_master, gc->gc_full, do_incremental,
                                    old_mem_use + old_gen0, gc->memory_in_use, 
                                    old_mem_allocated, mmu_memory_allocated(gc->mmu)+gc->phantom_count,
                                    gc->child_gc_total);
@@ -6135,7 +6140,7 @@ static void garbage_collect(NewGC *gc, int force_full, int no_full, int switchin
       if (sub_lmi.ran) {
         if (gc->GC_collect_inform_callback) {
           park_for_inform_callback(gc);
-          gc->GC_collect_inform_callback(1, sub_lmi.full,
+          gc->GC_collect_inform_callback(1, sub_lmi.full, 0,
                                          sub_lmi.pre_used, sub_lmi.post_used,
                                          sub_lmi.pre_admin, sub_lmi.post_admin,
                                          0);

racket/src/racket/include/mzwin.def

@@ -226,6 +226,7 @@ EXPORTS
  scheme_collect_garbage
  scheme_collect_garbage_minor
  scheme_enable_garbage_collection
+ scheme_incremental_garbage_collection
  scheme_malloc_immobile_box
  scheme_free_immobile_box
  scheme_add_gc_callback

racket/src/racket/include/mzwin3m.def

@@ -234,6 +234,7 @@ EXPORTS
  scheme_collect_garbage
  scheme_collect_garbage_minor
  scheme_enable_garbage_collection
+ scheme_incremental_garbage_collection
  GC_variable_stack
  GC_register_traversers
  GC_resolve

racket/src/racket/include/racket.exp

@@ -237,6 +237,7 @@ scheme_gc_ptr_ok
 scheme_collect_garbage
 scheme_collect_garbage_minor
 scheme_enable_garbage_collection
+scheme_incremental_garbage_collection
 GC_register_traversers
 GC_resolve
 GC_mark

racket/src/racket/include/racket3m.exp

@@ -241,6 +241,7 @@ scheme_gc_ptr_ok
 scheme_collect_garbage
 scheme_collect_garbage_minor
 scheme_enable_garbage_collection
+scheme_incremental_garbage_collection
 GC_variable_stack
 GC_register_traversers
 GC_resolve

racket/src/racket/src/salloc.c

@@ -1658,6 +1658,13 @@ void scheme_enable_garbage_collection(int on)
 #endif
 }
 
+void scheme_incremental_garbage_collection(int on)
+{
+#ifdef MZ_PRECISE_GC
+  GC_set_incremental_mode(on);
+#endif
+}
+
 MZ_DO_NOT_INLINE(uintptr_t scheme_get_deeper_address(void));
 
 uintptr_t scheme_get_deeper_address(void)

racket/src/racket/src/schemef.h

@@ -464,6 +464,7 @@ MZ_EXTERN void scheme_gc_ptr_ok(void *p);
 MZ_EXTERN void scheme_collect_garbage(void);
 MZ_EXTERN void scheme_collect_garbage_minor(void);
 MZ_EXTERN void scheme_enable_garbage_collection(int on);
+MZ_EXTERN void scheme_incremental_garbage_collection(int on);
 
 #ifdef MZ_PRECISE_GC
 # ifndef USE_THREAD_LOCAL

racket/src/racket/src/schemex.h

@@ -363,6 +363,7 @@ void (*scheme_gc_ptr_ok)(void *p);
 void (*scheme_collect_garbage)(void);
 void (*scheme_collect_garbage_minor)(void);
 void (*scheme_enable_garbage_collection)(int on);
+void (*scheme_incremental_garbage_collection)(int on);
 #ifdef MZ_PRECISE_GC
 # ifndef USE_THREAD_LOCAL
 void **GC_variable_stack;

racket/src/racket/src/schemex.inc

@@ -263,6 +263,7 @@
   scheme_extension_table->scheme_collect_garbage = scheme_collect_garbage;
   scheme_extension_table->scheme_collect_garbage_minor = scheme_collect_garbage_minor;
   scheme_extension_table->scheme_enable_garbage_collection = scheme_enable_garbage_collection;
+  scheme_extension_table->scheme_incremental_garbage_collection = scheme_incremental_garbage_collection;
 #ifdef MZ_PRECISE_GC
 # ifndef USE_THREAD_LOCAL
   scheme_extension_table->GC_variable_stack = GC_variable_stack;

racket/src/racket/src/schemexm.h

@@ -263,6 +263,7 @@
 #define scheme_collect_garbage (scheme_extension_table->scheme_collect_garbage)
 #define scheme_collect_garbage_minor (scheme_extension_table->scheme_collect_garbage_minor)
 #define scheme_enable_garbage_collection (scheme_extension_table->scheme_enable_garbage_collection)
+#define scheme_incremental_garbage_collection (scheme_extension_table->scheme_incremental_garbage_collection)
 #ifdef MZ_PRECISE_GC
 # ifndef USE_THREAD_LOCAL
 #define GC_variable_stack (scheme_extension_table->GC_variable_stack)

racket/src/racket/src/thread.c

@@ -223,7 +223,7 @@ THREAD_LOCAL_DECL(static double end_this_gc_real_time);
 static void get_ready_for_GC(void);
 static void done_with_GC(void);
 #ifdef MZ_PRECISE_GC
-static void inform_GC(int master_gc, int major_gc, intptr_t pre_used, intptr_t post_used,
+static void inform_GC(int master_gc, int major_gc, int inc_gc, intptr_t pre_used, intptr_t post_used,
                       intptr_t pre_admin, intptr_t post_admin, intptr_t post_child_places_used);
 #endif
 
@@ -9252,7 +9252,7 @@ static char *gc_num(char *nums, intptr_t v)
 END_XFORM_SKIP;
 #endif
 
-static void inform_GC(int master_gc, int major_gc, 
+static void inform_GC(int master_gc, int major_gc, int inc_gc,
                       intptr_t pre_used, intptr_t post_used,
                       intptr_t pre_admin, intptr_t post_admin,
                       intptr_t post_child_places_used)
@@ -9282,7 +9282,9 @@ static void inform_GC(int master_gc, int major_gc,
     vec = scheme_false;
     if (!master_gc && gc_info_prefab) {
       vec = scheme_make_vector(11, scheme_false);
-      SCHEME_VEC_ELS(vec)[1] = (major_gc ? scheme_true : scheme_false);
+      SCHEME_VEC_ELS(vec)[1] = (major_gc
+                                ? major_symbol
+                                : (inc_gc ? incremental_symbol : minor_symbol));
       SCHEME_VEC_ELS(vec)[2] = scheme_make_integer(pre_used);
       SCHEME_VEC_ELS(vec)[3] = scheme_make_integer(pre_admin);
       SCHEME_VEC_ELS(vec)[4] = scheme_make_integer(scheme_code_page_total);
@@ -9311,7 +9313,7 @@ static void inform_GC(int master_gc, int major_gc,
 #ifdef MZ_USE_PLACES
             scheme_current_place_id,
 #endif
-            (master_gc ? "MST" : (major_gc ? "MAJ" : "min")),
+            (master_gc ? "MST" : (major_gc ? "MAJ" : (inc_gc ? "mIn" : "min"))),
             gc_num(nums, pre_used), gc_num(nums, pre_admin - pre_used),
             gc_num(nums, scheme_code_page_total),
             gc_num(nums, delta), ((admin_delta < 0) ? "" : "+"),  gc_num(nums, admin_delta),