Allocate GC context in GC-managed heap

bdw.h

@@ -45,7 +45,7 @@ static inline void* get_field(void **addr) {
   return *addr;
 }
 
-static inline void initialize_gc(struct context* cx, size_t heap_size) {
+static struct context* initialize_gc(size_t heap_size) {
   // GC_full_freq = 30;
   // GC_free_space_divisor = 16;
   // GC_enable_incremental();
@@ -55,6 +55,7 @@ static inline void initialize_gc(struct context* cx, size_t heap_size) {
     GC_set_max_heap_size (heap_size);
     GC_expand_hp(heap_size - current_heap_size);
   }
+  return GC_malloc_atomic(1);
 }
 
 static inline void print_start_gc_stats(struct context *cx) {

gcbench.c

@@ -233,9 +233,12 @@ int main() {
     return 1;
   }
 
-  struct context _cx;
-  struct context *cx = &_cx;
-  initialize_gc(cx, kHeapSize);
+  struct context *cx = initialize_gc(kHeapSize);
+  if (!cx) {
+    fprintf(stderr, "Failed to initialize GC with heap size %zu bytes\n",
+            kHeapSize);
+    return 1;
+  }
 
   NodeHandle root = { NULL };
   NodeHandle longLivedTree = { NULL };

mark-sweep.h

@@ -107,9 +107,11 @@ struct context {
   uintptr_t base;
   uint8_t *mark_bytes;
   uintptr_t heap_base;
-  size_t size;
+  size_t heap_size;
   uintptr_t sweep;
   struct handle *roots;
+  void *mem;
+  size_t mem_size;
   long count;
   struct marker marker;
 };
@@ -133,8 +135,9 @@ static inline void clear_memory(uintptr_t addr, size_t size) {
 static void collect(struct context *cx) NEVER_INLINE;
 
 static inline uint8_t* mark_byte(struct context *cx, struct gcobj *obj) {
+  ASSERT(cx->heap_base <= (uintptr_t) obj);
+  ASSERT((uintptr_t) obj < cx->heap_base + cx->heap_size);
   uintptr_t granule = (((uintptr_t) obj) - cx->heap_base)  / GRANULE_SIZE;
-  ASSERT(granule < (cx->heap_base - cx->base));
   return &cx->mark_bytes[granule];
 }
 
@@ -284,7 +287,7 @@ static int sweep(struct context *cx, size_t for_granules) {
   // the end of the heap.
   ssize_t to_reclaim = 128;
   uintptr_t sweep = cx->sweep;
-  uintptr_t limit = cx->base + cx->size;
+  uintptr_t limit = cx->heap_base + cx->heap_size;
 
   if (sweep == limit)
     return 0;
@@ -339,7 +342,7 @@ static void* allocate_large(struct context *cx, enum alloc_kind kind,
 
     // No large object, and we swept across the whole heap.  Collect.
     if (swept_from_beginning) {
-      fprintf(stderr, "ran out of space, heap size %zu\n", cx->size);
+      fprintf(stderr, "ran out of space, heap size %zu\n", cx->heap_size);
       abort();
     } else {
       collect(cx);
@@ -379,7 +382,7 @@ static void fill_small(struct context *cx, enum small_object_size kind) {
 
     if (!sweep(cx, LARGE_OBJECT_GRANULE_THRESHOLD)) {
       if (swept_from_beginning) {
-        fprintf(stderr, "ran out of space, heap size %zu\n", cx->size);
+        fprintf(stderr, "ran out of space, heap size %zu\n", cx->heap_size);
         abort();
       } else {
         collect(cx);
@@ -425,7 +428,7 @@ static inline void* get_field(void **addr) {
   return *addr;
 }
 
-static inline void initialize_gc(struct context *cx, size_t size) {
+static struct context* initialize_gc(size_t size) {
 #define SMALL_OBJECT_GRANULE_SIZE(i) \
     ASSERT_EQ(SMALL_OBJECT_##i, small_object_sizes_for_granules[i]); \
     ASSERT_EQ(SMALL_OBJECT_##i + 1, small_object_sizes_for_granules[i+1]);
@@ -443,18 +446,34 @@ static inline void initialize_gc(struct context *cx, size_t size) {
     perror("mmap failed");
     abort();
   }
+
+  struct context *cx = mem;
+  cx->mem = mem;
+  cx->mem_size = size;
+  size_t overhead = sizeof(*cx);
+  // If there is 1 mark byte per granule, and SIZE bytes available for
+  // HEAP_SIZE + MARK_BYTES, then:
+  //
+  //   size = (granule_size + 1) / granule_size * heap_size
+  //   mark_bytes = 1/granule_size * heap_size
+  //   mark_bytes = ceil(size / (granule_size + 1))
+  cx->mark_bytes = ((uint8_t *)mem) + overhead;
+  size_t mark_bytes_size = (size - overhead + GRANULE_SIZE) / (GRANULE_SIZE + 1);
+  overhead += mark_bytes_size;
+  overhead = align_up(overhead, GRANULE_SIZE);
+
+  cx->heap_base = ((uintptr_t) mem) + overhead;
+  cx->heap_size = size - overhead;
+
   clear_freelists(cx);
-  cx->base = (uintptr_t) mem;
-  cx->mark_bytes = mem;
-  size_t heap_admin_size = align_up(size / GRANULE_SIZE, GRANULE_SIZE);
-  cx->heap_base = cx->base + heap_admin_size;
-  cx->size = size;
-  cx->sweep = cx->base + cx->size;
+  cx->sweep = cx->heap_base + cx->heap_size;
   cx->roots = NULL;
   cx->count = 0;
   if (!marker_init(cx))
     abort();
-  reclaim(cx, (void*)cx->heap_base, size_to_granules(size - heap_admin_size));
+  reclaim(cx, (void*)cx->heap_base, size_to_granules(cx->heap_size));
+
+  return cx;
 }
 
 static inline void print_start_gc_stats(struct context *cx) {
@@ -462,5 +481,5 @@ static inline void print_start_gc_stats(struct context *cx) {
 
 static inline void print_end_gc_stats(struct context *cx) {
   printf("Completed %ld collections\n", cx->count);
-  printf("Heap size is %zd\n", cx->size);
+  printf("Heap size with overhead is %zd\n", cx->mem_size);
 }

quads.c

@@ -127,9 +127,7 @@ int main(int argc, char *argv[]) {
   unsigned long gc_start = current_time();
   printf("Allocating heap of %.3fGB (%.2f multiplier of live data).\n",
          heap_size / 1e9, multiplier);
-  struct context _cx;
-  struct context *cx = &_cx;
-  initialize_gc(cx, heap_size);
+  struct context *cx = initialize_gc(heap_size);
 
   QuadHandle quad = { NULL };
 

semi.h

@@ -9,9 +9,11 @@
 struct context {
   uintptr_t hp;
   uintptr_t limit;
-  uintptr_t base;
-  size_t size;
+  uintptr_t heap_base;
+  size_t heap_size;
   struct handle *roots;
+  void *mem;
+  size_t mem_size;
   long count;
 };
 
@@ -33,12 +35,12 @@ static void collect_for_alloc(struct context *cx, size_t bytes) NEVER_INLINE;
 static void visit(void **loc, void *visit_data);
 
 static void flip(struct context *cx) {
-  uintptr_t split = cx->base + (cx->size >> 1);
+  uintptr_t split = cx->heap_base + (cx->heap_size >> 1);
   if (cx->hp <= split) {
     cx->hp = split;
-    cx->limit = cx->base + cx->size;
+    cx->limit = cx->heap_base + cx->heap_size;
   } else {
-    cx->hp = cx->base;
+    cx->hp = cx->heap_base;
     cx->limit = split;
   }
   cx->count++;
@@ -106,13 +108,13 @@ static void collect(struct context *cx) {
   // fprintf(stderr, "pushed %zd bytes in roots\n", cx->hp - grey);
   while(grey < cx->hp)
     grey = scan(cx, grey);
-  // fprintf(stderr, "%zd bytes copied\n", (cx->size>>1)-(cx->limit-cx->hp));
+  // fprintf(stderr, "%zd bytes copied\n", (cx->heap_size>>1)-(cx->limit-cx->hp));
 
 }
 static void collect_for_alloc(struct context *cx, size_t bytes) {
   collect(cx);
   if (cx->limit - cx->hp < bytes) {
-    fprintf(stderr, "ran out of space, heap size %zu\n", cx->size);
+    fprintf(stderr, "ran out of space, heap size %zu\n", cx->mem_size);
     abort();
   }
 }
@@ -151,20 +153,24 @@ static inline void* get_field(void **addr) {
   return *addr;
 }
 
-static inline void initialize_gc(struct context *cx, size_t size) {
-  size = align_up(size, getpagesize());
-
+static struct context* initialize_gc(size_t size) {
   void *mem = mmap(NULL, size, PROT_READ|PROT_WRITE,
                    MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
   if (mem == MAP_FAILED) {
     perror("mmap failed");
     abort();
   }
-  cx->hp = cx->base = (uintptr_t) mem;
-  cx->size = size;
+  struct context *cx = mem;
+  cx->mem = mem;
+  cx->mem_size = size;
+  // Round up to twice ALIGNMENT so that both spaces will be aligned.
+  size_t overhead = align_up(sizeof(*cx), ALIGNMENT * 2);
+  cx->hp = cx->heap_base = ((uintptr_t) mem) + overhead;
+  cx->heap_size = size - overhead;
   cx->count = -1;
   flip(cx);
   cx->roots = NULL;
+  return cx;
 }
 
 static inline void print_start_gc_stats(struct context *cx) {
@@ -172,5 +178,5 @@ static inline void print_start_gc_stats(struct context *cx) {
 
 static inline void print_end_gc_stats(struct context *cx) {
   printf("Completed %ld collections\n", cx->count);
-  printf("Heap size is %zd\n", cx->size);
+  printf("Heap size is %zd\n", cx->mem_size);
 }