Switch mark-sweep collector to mark stack

Slows down performance though!  Have to think here.

Makefile

@@ -14,7 +14,7 @@ bdw-%: bdw.h conservative-roots.h %.c
 semi-%: semi.h precise-roots.h %.c
 	$(CC) $(CFLAGS) -I. -DGC_SEMI -o $@ $*.c
 
-mark-sweep-%: mark-sweep.h precise-roots.h %.c
+mark-sweep-%: mark-sweep.h precise-roots.h serial-marker.h assert.h debug.h %.c
 	$(CC) $(CFLAGS) -I. -DGC_MARK_SWEEP -o $@ $*.c
 
 check: $(addprefix test-$(TARGET),$(TARGETS))

assert.h

@@ -0,0 +1,15 @@
+#ifndef ASSERT_H
+#define ASSERT_H
+
+#define STATIC_ASSERT_EQ(a, b) _Static_assert((a) == (b), "eq")
+
+#define UNLIKELY(e) __builtin_expect(e, 0)
+
+#ifndef NDEBUG
+#define ASSERT(x) do { if (UNLIKELY(!(x))) __builtin_trap(); } while (0)
+#else
+#define ASSERT(x) do { } while (0)
+#endif
+#define ASSERT_EQ(a,b) ASSERT((a) == (b))
+
+#endif // ASSERT_H

debug.h

@@ -0,0 +1,10 @@
+#ifndef DEBUG_H
+#define DEBUG_H
+
+#ifndef NDEBUG
+#define DEBUG(...) fprintf (stderr, "DEBUG: " __VA_ARGS__)
+#else
+#define DEBUG(...) do { } while (0)
+#endif
+
+#endif // DEBUG_H

mark-sweep.h

@@ -4,16 +4,9 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include "assert.h"
 #include "precise-roots.h"
-
+#include "serial-marker.h"
-#define STATIC_ASSERT_EQ(a, b) _Static_assert((a) == (b), "eq")
-
-#ifndef NDEBUG
-#define ASSERT(x) do { if (!(x)) __builtin_trap(); } while (0)
-#else
-#define ASSERT(x) do { } while (0)
-#endif
-#define ASSERT_EQ(a,b) ASSERT((a) == (b))
 
 #define GRANULE_SIZE 8
 #define GRANULE_SIZE_LOG_2 3
@@ -163,8 +156,13 @@ struct context {
   uintptr_t sweep;
   struct handle *roots;
   long count;
+  struct marker marker;
 };
 
+static inline struct marker* context_marker(struct context *cx) {
+  return &cx->marker;
+}
+
 static inline struct gcobj_free**
 get_small_object_freelist(struct context *cx, enum small_object_size kind) {
   ASSERT(kind < SMALL_OBJECT_SIZES);
@@ -187,27 +185,21 @@ static inline void clear_memory(uintptr_t addr, size_t size) {
 }
 
 static void collect(struct context *cx) __attribute__((noinline));
-static void mark(struct context *cx, void *p);
 
-static inline void visit(struct context *cx, void **loc) {
+static inline int mark_object(struct gcobj *obj) {
-  mark(cx, *loc);
+  if (tag_marked(obj->tag))
+    return 0;
+  tag_set_marked(&obj->tag);
+  return 1;
 }
 
-static void mark(struct context *cx, void *p) {
+static void process(struct context *cx, struct gcobj *obj) {
-  // A production mark implementation would use a worklist, to avoid
-  // stack overflow.  This implementation just uses the call stack.
-  struct gcobj *obj = p;
-  if (obj == NULL)
-    return;
-  if (tag_marked(obj->tag))
-    return;
-  tag_set_marked(&obj->tag);
   switch (tag_live_alloc_kind(obj->tag)) {
   case NODE:
-    visit_node_fields(cx, obj, visit);
+    visit_node_fields(cx, obj, marker_visit);
     break;
   case DOUBLE_ARRAY:
-    visit_double_array_fields(cx, obj, visit);
+    visit_double_array_fields(cx, obj, marker_visit);
     break;
   default:
     abort ();
@@ -223,8 +215,11 @@ static void clear_freelists(struct context *cx) {
 
 static void collect(struct context *cx) {
   // fprintf(stderr, "start collect #%ld:\n", cx->count);
+  marker_prepare(cx);
   for (struct handle *h = cx->roots; h; h = h->next)
-    mark(cx, h->v);
+    marker_visit_root(cx, &h->v);
+  marker_trace(cx, process);
+  marker_release(cx);
   // fprintf(stderr, "done marking\n");
   cx->sweep = cx->base;
   clear_freelists(cx);
@@ -513,6 +508,8 @@ static inline void initialize_gc(struct context *cx, size_t size) {
   cx->sweep = cx->base + cx->size;
   cx->roots = NULL;
   cx->count = 0;
+  if (!marker_init(cx))
+    abort();
   reclaim(cx, mem, size_to_granules(size));
 }
 

serial-marker.h

@@ -0,0 +1,136 @@
+#ifndef SERIAL_TRACE_H
+#define SERIAL_TRACE_H
+
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "assert.h"
+#include "debug.h"
+
+struct mark_stack {
+  size_t size;
+  size_t next;
+  uintptr_t *buf;
+};
+
+static const size_t mark_stack_max_size =
+  (1ULL << (sizeof(uintptr_t) * 8 - 1)) / sizeof(uintptr_t);
+static const size_t mark_stack_release_byte_threshold = 1 * 1024 * 1024;
+
+static void*
+mark_stack_alloc(size_t size) {
+  void *mem = mmap(NULL, size, PROT_READ|PROT_WRITE,
+                   MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+  if (mem == MAP_FAILED) {
+    perror("Failed to grow mark stack");
+    DEBUG("Failed to allocate %zu bytes", size);
+    return NULL;
+  }
+  return mem;
+}
+
+static int
+mark_stack_init(struct mark_stack *stack) {
+  stack->size = getpagesize();
+  stack->next = 0;
+  stack->buf = mark_stack_alloc(stack->size);
+  return !!stack->buf;
+}
+  
+static int
+mark_stack_grow(struct mark_stack *stack) {
+  uintptr_t size = stack->size;
+  if (size >= mark_stack_max_size) {
+    DEBUG("mark stack already at max size of %zu bytes", size);
+    return 0;
+  }
+  size *= 2;
+  uintptr_t *buf = mark_stack_alloc(size);
+  if (!buf)
+    return 0;
+  memcpy(buf, stack->buf, stack->next * sizeof(uintptr_t));
+  munmap(stack->buf, stack->size * sizeof(uintptr_t));
+  stack->size = size;
+  stack->buf = buf;
+  return 1;
+}
+  
+static inline void
+mark_stack_push(struct mark_stack *stack, void *p) {
+  size_t next = stack->next;
+  if (UNLIKELY(next == stack->size)) {
+    if (!mark_stack_grow(stack))
+      abort();
+  }
+  stack->buf[next] = (uintptr_t)p;
+  stack->next = next + 1;
+}
+
+static inline void*
+mark_stack_pop(struct mark_stack *stack) {
+  size_t next = stack->next;
+  if (UNLIKELY(next == 0))
+    return NULL;
+  uintptr_t ret = stack->buf[next - 1];
+  stack->next = next - 1;
+  return (void*)ret;
+}
+
+static void
+mark_stack_release(struct mark_stack *stack) {
+  size_t byte_size = stack->size * sizeof(uintptr_t);
+  if (byte_size >= mark_stack_release_byte_threshold)
+    madvise(stack->buf, byte_size, MADV_DONTNEED);
+}
+
+static void
+mark_stack_destroy(struct mark_stack *stack) {
+  size_t byte_size = stack->size * sizeof(uintptr_t);
+  munmap(stack->buf, byte_size);
+}
+
+struct marker {
+  struct mark_stack stack;
+};
+
+struct context;
+static inline struct marker* context_marker(struct context *cx);
+
+static int
+marker_init(struct context *cx) {
+  return mark_stack_init(&context_marker(cx)->stack);
+}
+static void marker_prepare(struct context *cx) {}
+static void marker_release(struct context *cx) {
+  mark_stack_release(&context_marker(cx)->stack);
+}
+
+struct gcobj;
+static inline void marker_visit(struct context *cx, void **loc) __attribute__((always_inline));
+static inline void marker_trace(struct context *cx,
+                                void (*)(struct context *, struct gcobj *))
+  __attribute__((always_inline));
+static inline int mark_object(struct gcobj *obj) __attribute__((always_inline));
+
+static inline void
+marker_visit(struct context *cx, void **loc) {
+  struct gcobj *obj = *loc;
+  if (obj) {
+    __builtin_prefetch(obj);
+    mark_stack_push(&context_marker(cx)->stack, obj);
+  }
+}
+static inline void
+marker_visit_root(struct context *cx, void **loc) {
+  marker_visit(cx, loc);
+}
+static inline void
+marker_trace(struct context *cx,
+             void (*process)(struct context *, struct gcobj *)) {
+  struct gcobj *obj;
+  while ((obj = mark_stack_pop(&context_marker(cx)->stack)))
+    if (mark_object(obj))
+      process(cx, obj);
+}
+
+#endif // SERIAL_MARK_H