Fix shared-space marked-page chaining

Fixes a problem with a4910716e4, and adjusts place-specific
major GCs to use the already constructed chain instead
of reconstructing it.

racket/src/racket/gc2/newgc.c

@@ -84,7 +84,7 @@ enum {
   PAGE_PAIR     = 4,
   PAGE_BIG      = 5,
   /* the number of page types: */
-  PAGE_TYPES    = 6,
+  PAGE_TYPES    = 6
 };
 
 enum {
@@ -120,7 +120,8 @@ enum {
 enum {
   AGE_GEN_0    = 0,
   AGE_GEN_HALF = 1,
-  AGE_GEN_1    = 2
+  AGE_GEN_1    = 2,
+  AGE_VACATED  = 3
 };
 
 static const char *type_name[PAGE_TYPES] = {
@@ -1678,12 +1679,12 @@ int GC_allocate_phantom_bytes(void *pb, intptr_t request_size_bytes)
     request_size_bytes = -request_size_bytes;
     if (gc->memory_in_use > request_size_bytes)
       gc->memory_in_use -= request_size_bytes;
-    if (!page || (page->generation != AGE_GEN_1)) {
+    if (!page || (page->generation < AGE_GEN_1)) {
       if (gc->gen0_phantom_count > request_size_bytes)
         gc->gen0_phantom_count -= request_size_bytes;
     }
   } else {
-    if (!page || (page->generation != AGE_GEN_1))
+    if (!page || (page->generation < AGE_GEN_1))
       gc->gen0_phantom_count = add_no_overflow(gc->gen0_phantom_count, request_size_bytes);
     gc->memory_in_use = add_no_overflow(gc->memory_in_use, request_size_bytes);
   }
@@ -4301,6 +4302,8 @@ mpage *allocate_compact_target(NewGC *gc, mpage *work)
   npage->size_class = SIZE_CLASS_SMALL_PAGE;
   npage->page_type = work->page_type;
   npage->marked_on = 1;
+  npage->modified_next = gc->modified_next;
+  gc->modified_next = npage;
   backtrace_new_page(gc, npage);
   pagemap_add(gc->page_maps, npage);
   gc->num_gen1_pages++;
@@ -4411,6 +4414,9 @@ inline static void do_heap_compact(NewGC *gc)
           /* push work onto gc->release_pages */
           work->next = gc->release_pages;
           gc->release_pages = work;
+          /* Setting the generation causes `work` to be ignored
+             in the `modified_next` chain: */
+          work->generation = AGE_VACATED;
 
           work = prev;
         } else { 
@@ -4490,7 +4496,9 @@ static int repair_mixed_page(NewGC *gc, mpage *page, void **end)
 }
 
 static void chain_marked_on(NewGC *gc)
-/* add any page that is marked on to the `modified_next` chain */
+/* add any page that is marked on to the `modified_next` chain; this
+   is needed for a master GC, because the place GCs do not register
+   marked master pages in the master GC's `modified_next` chain */
 {
   mpage *page;
   int i, ty;
@@ -4499,6 +4507,7 @@ static void chain_marked_on(NewGC *gc)
 
   for (i = 0; i < PAGE_TYPES; i++) {
     for (page = gc->gen1_pages[i]; page; page = page->next) {
+      GC_ASSERT(!page->marked_from);
       if (page->marked_on) {
         page->modified_next = gc->modified_next;
         gc->modified_next = page;
@@ -4509,6 +4518,7 @@ static void chain_marked_on(NewGC *gc)
   for (ty = 0; ty < MED_PAGE_TYPES; ty++) {
     for (i = 0; i < NUM_MED_PAGE_SIZES; i++) {
       for (page = gc->med_pages[ty][i]; page; page = page->next) {
+        GC_ASSERT(!page->marked_from);
         if (page->marked_on) {
           page->modified_next = gc->modified_next;
           gc->modified_next = page;
@@ -4518,6 +4528,51 @@ static void chain_marked_on(NewGC *gc)
   }
 }
 
+#if 0
+# define CHECK_MARKED_ON_IN_MODIFIED_CHAIN
+static void chain_marked_on_check(NewGC *gc)
+{
+  mpage *page, *xpage;
+  int i, ty, found = 0;
+
+  for (i = 0; i < PAGE_TYPES; i++) {
+    for (page = gc->gen1_pages[i]; page; page = page->next) {
+      if (page->marked_on) {
+        for (xpage = gc->modified_next; xpage; xpage = xpage->modified_next) {
+          if (xpage == page)
+            break;
+        }
+        GC_ASSERT(xpage);
+        found++;
+      }
+    }
+  }
+
+  for (ty = 0; ty < MED_PAGE_TYPES; ty++) {
+    for (i = 0; i < NUM_MED_PAGE_SIZES; i++) {
+      for (page = gc->med_pages[ty][i]; page; page = page->next) {
+        if (page->marked_on) {
+          for (xpage = gc->modified_next; xpage; xpage = xpage->modified_next) {
+            if (xpage == page)
+              break;
+          }
+          GC_ASSERT(xpage);
+          found++;
+        }
+      }
+    }
+  }
+
+  for (xpage = gc->modified_next; xpage; xpage = xpage->modified_next) {
+    if (xpage->generation < AGE_VACATED)
+      --found;
+  }
+  GC_ASSERT(!found);
+}
+#else
+static void chain_marked_on_check(NewGC *gc) { }
+#endif
+
 static void repair_heap(NewGC *gc)
 {
   uintptr_t memory_in_use;
@@ -4538,6 +4593,9 @@ static void repair_heap(NewGC *gc)
   for (; page; page = next) {
     GC_ASSERT(page->marked_on || page->marked_from);
     next = page->modified_next;
+    if (page->generation == AGE_VACATED) {
+      /* this page will be released later */
+    } else {
       page->has_new = 0;
       if (gc->gc_full)
         page->marked_on = 1;
@@ -4683,6 +4741,7 @@ static void repair_heap(NewGC *gc)
       else
         page->back_pointers = 0;
     }
+  }
 
   /* All gen-half pages count as modified: */
   for (page = gc->gen_half.pages; page; page = page->next) {
@@ -5154,8 +5213,10 @@ static void garbage_collect(NewGC *gc, int force_full, int no_full, int switchin
   if (premaster_or_place_gc(gc))
     GC_fixup_variable_stack(GC_variable_stack, 0, get_stack_base(gc), NULL);
   TIME_STEP("reparied roots");
-  if (gc->gc_full && postmaster_and_place_gc(gc))
+  if (gc->gc_full && postmaster_and_master_gc(gc))
     chain_marked_on(gc);
+  else if (gc->gc_full)
+    chain_marked_on_check(gc);
   repair_heap(gc);
   TIME_STEP("repaired");
   clean_up_heap(gc);