text: /*
   * sgen-marksweep.c: The Mark & Sweep major collector.
   *
   * Author:
   * 	Mark Probst <mark.probst@gmail.com>
   *
   * Copyright 2009-2010 Novell, Inc.
   * Copyright (C) 2012 Xamarin Inc
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Library General Public
   * License 2.0 as published by the Free Software Foundation;
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Library General Public License for more details.
   *
   * You should have received a copy of the GNU Library General Public
   * License 2.0 along with this library; if not, write to the Free
   * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  
  #include "config.h"
  
  #ifdef HAVE_SGEN_GC
  
  #include <math.h>
  #include <errno.h>
  #include <string.h>
  #include <stdlib.h>
  
  #include "mono/sgen/sgen-gc.h"
  #include "mono/sgen/sgen-protocol.h"
  #include "mono/sgen/sgen-cardtable.h"
  #include "mono/sgen/sgen-memory-governor.h"
  #include "mono/sgen/sgen-layout-stats.h"
  #include "mono/sgen/sgen-pointer-queue.h"
  #include "mono/sgen/sgen-pinning.h"
  #include "mono/sgen/sgen-workers.h"
  #include "mono/sgen/sgen-thread-pool.h"
  #include "mono/sgen/sgen-client.h"
  #include "mono/utils/mono-membar.h"
  
  #if defined(ARCH_MIN_MS_BLOCK_SIZE) && defined(ARCH_MIN_MS_BLOCK_SIZE_SHIFT)
  #define MS_BLOCK_SIZE	ARCH_MIN_MS_BLOCK_SIZE
  #define MS_BLOCK_SIZE_SHIFT	ARCH_MIN_MS_BLOCK_SIZE_SHIFT
  #else
  #define MS_BLOCK_SIZE_SHIFT     14      /* INT FASTENABLE */
  #define MS_BLOCK_SIZE           (1 << MS_BLOCK_SIZE_SHIFT)
  #endif
  #define MAJOR_SECTION_SIZE	MS_BLOCK_SIZE
  #define CARDS_PER_BLOCK (MS_BLOCK_SIZE / CARD_SIZE_IN_BYTES)
  
  /*
   * Don't allocate single blocks, but alloc a contingent of this many
   * blocks in one swoop.  This must be a power of two.
   */
  #define MS_BLOCK_ALLOC_NUM	32
  
  /*
   * Number of bytes before the first object in a block.  At the start
   * of a block is the MSBlockHeader, then opional padding, then come
   * the objects, so this must be >= sizeof (MSBlockHeader).
   */
  #define MS_BLOCK_SKIP	((sizeof (MSBlockHeader) + 15) & ~15)
  
  #define MS_BLOCK_FREE	(MS_BLOCK_SIZE - MS_BLOCK_SKIP)
  
  #define MS_NUM_MARK_WORDS	((MS_BLOCK_SIZE / SGEN_ALLOC_ALIGN + sizeof (mword) * 8 - 1) / (sizeof (mword) * 8))
  
  /*
   * Blocks progress from one state to the next:
   *
   * SWEPT           The block is fully swept.  It might or might not be in
   *                 a free list.
   *
   * MARKING         The block might or might not contain live objects.  If
   *                 we're in between an initial collection pause and the
   *                 finishing pause, the block might or might not be in a
   *                 free list.
   *
   * CHECKING        The sweep thread is investigating the block to determine
   *                 whether or not it contains live objects.  The block is
   *                 not in a free list.
   *
   * NEED_SWEEPING   The block contains live objects but has not yet been
   *                 swept.  It also contains free slots.  It is in a block
   *                 free list.
   *
   * SWEEPING        The block is being swept.  It might be in a free list.
   */
  
  enum {
  	BLOCK_STATE_SWEPT,
  	BLOCK_STATE_MARKING,
  	BLOCK_STATE_CHECKING,
  	BLOCK_STATE_NEED_SWEEPING,
  	BLOCK_STATE_SWEEPING
  };
  
  typedef struct _MSBlockInfo MSBlockInfo;
  struct _MSBlockInfo {
  	guint16 obj_size;
  	/*
  	 * FIXME: Do we even need this? It's only used during sweep and might be worth
  	 * recalculating to save the space.
  	 */
  	guint16 obj_size_index;
  	/* FIXME: Reduce this - it only needs a byte. */
  	volatile gint32 state;
  	unsigned int pinned : 1;
  	unsigned int has_references : 1;
  	unsigned int has_pinned : 1;	/* means cannot evacuate */
  	unsigned int is_to_space : 1;
  	void ** volatile free_list;
  	MSBlockInfo * volatile next_free;
  	guint8 * volatile cardtable_mod_union;
  	mword mark_words [MS_NUM_MARK_WORDS];
  };
  
  #define MS_BLOCK_FOR_BLOCK_INFO(b)	((char*)(b))
  
  #define MS_BLOCK_OBJ(b,i)		((void*)(MS_BLOCK_FOR_BLOCK_INFO(b) + MS_BLOCK_SKIP + (b)->obj_size * (i)))
  #define MS_BLOCK_OBJ_FOR_SIZE(b,i,obj_size)		(MS_BLOCK_FOR_BLOCK_INFO(b) + MS_BLOCK_SKIP + (obj_size) * (i))
  #define MS_BLOCK_DATA_FOR_OBJ(o)	((char*)((mword)(o) & ~(mword)(MS_BLOCK_SIZE - 1)))
  
  typedef struct {
  	MSBlockInfo info;
  } MSBlockHeader;
  
  #define MS_BLOCK_FOR_OBJ(o)		(&((MSBlockHeader*)MS_BLOCK_DATA_FOR_OBJ ((o)))->info)
  
  /* object index will always be small */
  #define MS_BLOCK_OBJ_INDEX(o,b)	((int)(((char*)(o) - (MS_BLOCK_FOR_BLOCK_INFO(b) + MS_BLOCK_SKIP)) / (b)->obj_size))
  
  //casting to int is fine since blocks are 32k
  #define MS_CALC_MARK_BIT(w,b,o) 	do {				\
  		int i = ((int)((char*)(o) - MS_BLOCK_DATA_FOR_OBJ ((o)))) >> SGEN_ALLOC_ALIGN_BITS; \
  		if (sizeof (mword) == 4) {				\
  			(w) = i >> 5;					\
  			(b) = i & 31;					\
  		} else {						\
  			(w) = i >> 6;					\
  			(b) = i & 63;					\
  		}							\
  	} while (0)
  
  #define MS_MARK_BIT(bl,w,b)	((bl)->mark_words [(w)] & (ONE_P << (b)))
  #define MS_SET_MARK_BIT(bl,w,b)	((bl)->mark_words [(w)] |= (ONE_P << (b)))
  
  #define MS_OBJ_ALLOCED(o,b)	(*(void**)(o) && (*(char**)(o) < MS_BLOCK_FOR_BLOCK_INFO (b) || *(char**)(o) >= MS_BLOCK_FOR_BLOCK_INFO (b) + MS_BLOCK_SIZE))
  
  #define MS_BLOCK_OBJ_SIZE_FACTOR	(pow (2.0, 1.0 / 3))
  
  /*
   * This way we can lookup block object size indexes for sizes up to
   * 256 bytes with a single load.
   */
  #define MS_NUM_FAST_BLOCK_OBJ_SIZE_INDEXES	32
  
  static int *block_obj_sizes;
  static int num_block_obj_sizes;
  static int fast_block_obj_size_indexes [MS_NUM_FAST_BLOCK_OBJ_SIZE_INDEXES];
  
  #define MS_BLOCK_FLAG_PINNED	1
  #define MS_BLOCK_FLAG_REFS	2
  
  #define MS_BLOCK_TYPE_MAX	4
  
  static gboolean *evacuate_block_obj_sizes;
  static float evacuation_threshold = 0.666f;
  static float concurrent_evacuation_threshold = 0.666f;
  static gboolean want_evacuation = FALSE;
  
  static gboolean lazy_sweep = FALSE;
  
  enum {
  	SWEEP_STATE_SWEPT,
  	SWEEP_STATE_NEED_SWEEPING,
  	SWEEP_STATE_SWEEPING,
  	SWEEP_STATE_SWEEPING_AND_ITERATING,
  	SWEEP_STATE_COMPACTING
  };
  
  static volatile int sweep_state = SWEEP_STATE_SWEPT;
  
  static gboolean concurrent_mark;
  static gboolean concurrent_sweep = TRUE;
  
  #define BLOCK_IS_TAGGED_HAS_REFERENCES(bl)	SGEN_POINTER_IS_TAGGED_1 ((bl))
  #define BLOCK_TAG_HAS_REFERENCES(bl)		SGEN_POINTER_TAG_1 ((bl))
  
  #define BLOCK_IS_TAGGED_CHECKING(bl)		SGEN_POINTER_IS_TAGGED_2 ((bl))
  #define BLOCK_TAG_CHECKING(bl)			SGEN_POINTER_TAG_2 ((bl))
  
  #define BLOCK_UNTAG(bl)				SGEN_POINTER_UNTAG_12 ((bl))
  
  #define BLOCK_TAG(bl)				((bl)->has_references ? BLOCK_TAG_HAS_REFERENCES ((bl)) : (bl))
  
  /* all allocated blocks in the system */
  static SgenPointerQueue allocated_blocks;
  
  /* non-allocated block free-list */
  static void *empty_blocks = NULL;
  static size_t num_empty_blocks = 0;
  
  #define FOREACH_BLOCK_NO_LOCK_CONDITION(cond,bl) {			\
  	size_t __index;							\
  	SGEN_ASSERT (0, (cond) && !sweep_in_progress (), "Can't iterate blocks while the world is running or sweep is in progress."); \
  	for (__index = 0; __index < allocated_blocks.next_slot; ++__index) { \
  		(bl) = BLOCK_UNTAG (allocated_blocks.data [__index]);
  #define FOREACH_BLOCK_NO_LOCK(bl)					\
  	FOREACH_BLOCK_NO_LOCK_CONDITION(sgen_is_world_stopped (), bl)
  #define FOREACH_BLOCK_HAS_REFERENCES_NO_LOCK(bl,hr) {			\
  	size_t __index;							\
  	SGEN_ASSERT (0, sgen_is_world_stopped () && !sweep_in_progress (), "Can't iterate blocks while the world is running or sweep is in progress."); \
  	for (__index = 0; __index < allocated_blocks.next_slot; ++__index) { \
  		(bl) = allocated_blocks.data [__index];			\
  		(hr) = BLOCK_IS_TAGGED_HAS_REFERENCES ((bl));		\
  		(bl) = BLOCK_UNTAG ((bl));
  #define END_FOREACH_BLOCK_NO_LOCK	} }
  
  static volatile size_t num_major_sections = 0;
  /*
   * One free block list for each block object size.  We add and remove blocks from these
   * lists lock-free via CAS.
   *
   * Blocks accessed/removed from `free_block_lists`:
   *   from the mutator (with GC lock held)
   *   in nursery collections
   *   in non-concurrent major collections
   *   in the finishing pause of concurrent major collections (whole list is cleared)
   *
   * Blocks added to `free_block_lists`:
   *   in the sweeping thread
   *   during nursery collections
   *   from domain clearing (with the world stopped and no sweeping happening)
   *
   * The only item of those that doesn't require the GC lock is the sweep thread.  The sweep
   * thread only ever adds blocks to the free list, so the ABA problem can't occur.
   */
  static MSBlockInfo * volatile *free_block_lists [MS_BLOCK_TYPE_MAX];
  
  static guint64 stat_major_blocks_alloced = 0;
  static guint64 stat_major_blocks_freed = 0;
  static guint64 stat_major_blocks_lazy_swept = 0;
  static guint64 stat_major_objects_evacuated = 0;
  
  #if SIZEOF_VOID_P != 8
  static guint64 stat_major_blocks_freed_ideal = 0;
  static guint64 stat_major_blocks_freed_less_ideal = 0;
  static guint64 stat_major_blocks_freed_individual = 0;
  static guint64 stat_major_blocks_alloced_less_ideal = 0;
  #endif
  
  #ifdef SGEN_COUNT_NUMBER_OF_MAJOR_OBJECTS_MARKED
  static guint64 num_major_objects_marked = 0;
  #define INC_NUM_MAJOR_OBJECTS_MARKED()	(++num_major_objects_marked)
  #else
  #define INC_NUM_MAJOR_OBJECTS_MARKED()
  #endif
  
  #ifdef SGEN_HEAVY_BINARY_PROTOCOL
  static mono_mutex_t scanned_objects_list_lock;
  static SgenPointerQueue scanned_objects_list;
  
  static void
  add_scanned_object (void *ptr)
  {
  	if (!binary_protocol_is_enabled ())
  		return;
  
  	mono_os_mutex_lock (&scanned_objects_list_lock);
  	sgen_pointer_queue_add (&scanned_objects_list, ptr);
  	mono_os_mutex_unlock (&scanned_objects_list_lock);
  }
  #endif
  
  static gboolean sweep_block (MSBlockInfo *block);
  
  static int
  ms_find_block_obj_size_index (size_t size)
  {
  	int i;
  	SGEN_ASSERT (9, size <= SGEN_MAX_SMALL_OBJ_SIZE, "size %zd is bigger than max small object size %d", size, SGEN_MAX_SMALL_OBJ_SIZE);
  	for (i = 0; i < num_block_obj_sizes; ++i)
  		if (block_obj_sizes [i] >= size)
  			return i;
  	g_error ("no object of size %zd\n", size);
  	return -1;
  }
  
  #define FREE_BLOCKS_FROM(lists,p,r)	(lists [((p) ? MS_BLOCK_FLAG_PINNED : 0) | ((r) ? MS_BLOCK_FLAG_REFS : 0)])
  #define FREE_BLOCKS(p,r)		(FREE_BLOCKS_FROM (free_block_lists, (p), (r)))
  
  #define MS_BLOCK_OBJ_SIZE_INDEX(s)				\
  	(((s)+7)>>3 < MS_NUM_FAST_BLOCK_OBJ_SIZE_INDEXES ?	\
  	 fast_block_obj_size_indexes [((s)+7)>>3] :		\
  	 ms_find_block_obj_size_index ((s)))
  
  static void*
  major_alloc_heap (mword nursery_size, mword nursery_align, int the_nursery_bits)
  {
  	char *start;
  	if (nursery_align)
  		start = sgen_alloc_os_memory_aligned (nursery_size, nursery_align, SGEN_ALLOC_HEAP | SGEN_ALLOC_ACTIVATE, "nursery");
  	else
  		start = sgen_alloc_os_memory (nursery_size, SGEN_ALLOC_HEAP | SGEN_ALLOC_ACTIVATE, "nursery");
  
  	return start;
  }
  
  static void
  update_heap_boundaries_for_block (MSBlockInfo *block)
  {
  	sgen_update_heap_boundaries ((mword)MS_BLOCK_FOR_BLOCK_INFO (block), (mword)MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE);
  }
  
  /*
   * Thread safe
   */
  static void*
  ms_get_empty_block (void)
  {
  	char *p;
  	int i;
  	void *block, *empty, *next;
  
   retry:
  	if (!empty_blocks) {
  		/*
  		 * We try allocating MS_BLOCK_ALLOC_NUM blocks first.  If that's
  		 * unsuccessful, we halve the number of blocks and try again, until we're at
  		 * 1.  If that doesn't work, either, we assert.
  		 */
  		int alloc_num = MS_BLOCK_ALLOC_NUM;
  		for (;;) {
  			p = sgen_alloc_os_memory_aligned (MS_BLOCK_SIZE * alloc_num, MS_BLOCK_SIZE, SGEN_ALLOC_HEAP | SGEN_ALLOC_ACTIVATE,
  					alloc_num == 1 ? "major heap section" : NULL);
  			if (p)
  				break;
  			alloc_num >>= 1;
  		}
  
  		for (i = 0; i < alloc_num; ++i) {
  			block = p;
  			/*
  			 * We do the free list update one after the
  			 * other so that other threads can use the new
  			 * blocks as quickly as possible.
  			 */
  			do {
  				empty = empty_blocks;
  				*(void**)block = empty;
  			} while (SGEN_CAS_PTR ((gpointer*)&empty_blocks, block, empty) != empty);
  			p += MS_BLOCK_SIZE;
  		}
  
  		SGEN_ATOMIC_ADD_P (num_empty_blocks, alloc_num);
  
  		stat_major_blocks_alloced += alloc_num;
  #if SIZEOF_VOID_P != 8
  		if (alloc_num != MS_BLOCK_ALLOC_NUM)
  			stat_major_blocks_alloced_less_ideal += alloc_num;
  #endif
  	}
  
  	do {
  		empty = empty_blocks;
  		if (!empty)
  			goto retry;
  		block = empty;
  		next = *(void**)block;
  	} while (SGEN_CAS_PTR (&empty_blocks, next, empty) != empty);
  
  	SGEN_ATOMIC_ADD_P (num_empty_blocks, -1);
  
  	*(void**)block = NULL;
  
  	g_assert (!((mword)block & (MS_BLOCK_SIZE - 1)));
  
  	return block;
  }
  
  /*
   * This doesn't actually free a block immediately, but enqueues it into the `empty_blocks`
   * list, where it will either be freed later on, or reused in nursery collections.
   */
  static void
  ms_free_block (void *block)
  {
  	void *empty;
  
  	sgen_memgov_release_space (MS_BLOCK_SIZE, SPACE_MAJOR);
  	memset (block, 0, MS_BLOCK_SIZE);
  
  	do {
  		empty = empty_blocks;
  		*(void**)block = empty;
  	} while (SGEN_CAS_PTR (&empty_blocks, block, empty) != empty);
  
  	SGEN_ATOMIC_ADD_P (num_empty_blocks, 1);
  
  	binary_protocol_block_free (block, MS_BLOCK_SIZE);
  }
  
  static gboolean
  sweep_in_progress (void)
  {
  	int state = sweep_state;
  	return state == SWEEP_STATE_SWEEPING ||
  		state == SWEEP_STATE_SWEEPING_AND_ITERATING ||
  		state == SWEEP_STATE_COMPACTING;
  }
  
  static inline gboolean
  block_is_swept_or_marking (MSBlockInfo *block)
  {
  	gint32 state = block->state;
  	return state == BLOCK_STATE_SWEPT || state == BLOCK_STATE_MARKING;
  }
  
  //#define MARKSWEEP_CONSISTENCY_CHECK
  
  #ifdef MARKSWEEP_CONSISTENCY_CHECK
  static void
  check_block_free_list (MSBlockInfo *block, int size, gboolean pinned)
  {
  	SGEN_ASSERT (0, !sweep_in_progress (), "Can't examine allocated blocks during sweep");
  	for (; block; block = block->next_free) {
  		SGEN_ASSERT (0, block->state != BLOCK_STATE_CHECKING, "Can't have a block we're checking in a free list.");
  		g_assert (block->obj_size == size);
  		g_assert ((pinned && block->pinned) || (!pinned && !block->pinned));
  
  		/* blocks in the free lists must have at least
  		   one free slot */
  		g_assert (block->free_list);
  
  		/* the block must be in the allocated_blocks array */
  		g_assert (sgen_pointer_queue_find (&allocated_blocks, BLOCK_TAG (block)) != (size_t)-1);
  	}
  }
  
  static void
  check_empty_blocks (void)
  {
  	void *p;
  	size_t i = 0;
  	for (p = empty_blocks; p; p = *(void**)p)
  		++i;
  	g_assert (i == num_empty_blocks);
  }
  
  static void
  consistency_check (void)
  {
  	MSBlockInfo *block;
  	int i;
  
  	/* check all blocks */
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int count = MS_BLOCK_FREE / block->obj_size;
  		int num_free = 0;
  		void **free;
  
  		/* count number of free slots */
  		for (i = 0; i < count; ++i) {
  			void **obj = (void**) MS_BLOCK_OBJ (block, i);
  			if (!MS_OBJ_ALLOCED (obj, block))
  				++num_free;
  		}
  
  		/* check free list */
  		for (free = block->free_list; free; free = (void**)*free) {
  			g_assert (MS_BLOCK_FOR_OBJ (free) == block);
  			--num_free;
  		}
  		g_assert (num_free == 0);
  
  		/* check all mark words are zero */
  		if (!sgen_concurrent_collection_in_progress () && block_is_swept_or_marking (block)) {
  			for (i = 0; i < MS_NUM_MARK_WORDS; ++i)
  				g_assert (block->mark_words [i] == 0);
  		}
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	/* check free blocks */
  	for (i = 0; i < num_block_obj_sizes; ++i) {
  		int j;
  		for (j = 0; j < MS_BLOCK_TYPE_MAX; ++j)
  			check_block_free_list (free_block_lists [j][i], block_obj_sizes [i], j & MS_BLOCK_FLAG_PINNED);
  	}
  
  	check_empty_blocks ();
  }
  #endif
  
  static void
  add_free_block (MSBlockInfo * volatile *free_blocks, int size_index, MSBlockInfo *block)
  {
  	MSBlockInfo *old;
  	do {
  		block->next_free = old = free_blocks [size_index];
  	} while (SGEN_CAS_PTR ((gpointer)&free_blocks [size_index], block, old) != old);
  }
  
  static void major_finish_sweep_checking (void);
  
  static gboolean
  ms_alloc_block (int size_index, gboolean pinned, gboolean has_references)
  {
  	int size = block_obj_sizes [size_index];
  	int count = MS_BLOCK_FREE / size;
  	MSBlockInfo *info;
  	MSBlockInfo * volatile * free_blocks = FREE_BLOCKS (pinned, has_references);
  	char *obj_start;
  	int i;
  
  	if (!sgen_memgov_try_alloc_space (MS_BLOCK_SIZE, SPACE_MAJOR))
  		return FALSE;
  
  	info = (MSBlockInfo*)ms_get_empty_block ();
  
  	SGEN_ASSERT (9, count >= 2, "block with %d objects, it must hold at least 2", count);
  
  	info->obj_size = size;
  	info->obj_size_index = size_index;
  	info->pinned = pinned;
  	info->has_references = has_references;
  	info->has_pinned = pinned;
  	/*
  	 * Blocks that are to-space are not evacuated from.  During an major collection
  	 * blocks are allocated for two reasons: evacuating objects from the nursery and
  	 * evacuating them from major blocks marked for evacuation.  In both cases we don't
  	 * want further evacuation.
  	 */
  	info->is_to_space = (sgen_get_current_collection_generation () == GENERATION_OLD);
  	info->state = (info->is_to_space || sgen_concurrent_collection_in_progress ()) ? BLOCK_STATE_MARKING : BLOCK_STATE_SWEPT;
  	SGEN_ASSERT (6, !sweep_in_progress () || info->state == BLOCK_STATE_SWEPT, "How do we add a new block to be swept while sweeping?");
  	info->cardtable_mod_union = NULL;
  
  	update_heap_boundaries_for_block (info);
  
  	binary_protocol_block_alloc (info, MS_BLOCK_SIZE);
  
  	/* build free list */
  	obj_start = MS_BLOCK_FOR_BLOCK_INFO (info) + MS_BLOCK_SKIP;
  	info->free_list = (void**)obj_start;
  	/* we're skipping the last one - it must be nulled */
  	for (i = 0; i < count - 1; ++i) {
  		char *next_obj_start = obj_start + size;
  		*(void**)obj_start = next_obj_start;
  		obj_start = next_obj_start;
  	}
  	/* the last one */
  	*(void**)obj_start = NULL;
  
  	add_free_block (free_blocks, size_index, info);
  
  	/*
  	 * Adding to the allocated_blocks array is racy with the removal of nulls when
  	 * sweeping. We wait for sweep to finish to avoid that.
  	 *
  	 * The memory barrier here and in `sweep_job_func()` are required because we need
  	 * `allocated_blocks` synchronized between this and the sweep thread.
  	 */
  	major_finish_sweep_checking ();
  	mono_memory_barrier ();
  
  	sgen_pointer_queue_add (&allocated_blocks, BLOCK_TAG (info));
  
  	SGEN_ATOMIC_ADD_P (num_major_sections, 1);
  	return TRUE;
  }
  
  static gboolean
  ptr_is_from_pinned_alloc (char *ptr)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		if (ptr >= MS_BLOCK_FOR_BLOCK_INFO (block) && ptr <= MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE)
  			return block->pinned;
  	} END_FOREACH_BLOCK_NO_LOCK;
  	return FALSE;
  }
  
  static void
  ensure_can_access_block_free_list (MSBlockInfo *block)
  {
   retry:
  	for (;;) {
  		switch (block->state) {
  		case BLOCK_STATE_SWEPT:
  		case BLOCK_STATE_MARKING:
  			return;
  		case BLOCK_STATE_CHECKING:
  			SGEN_ASSERT (0, FALSE, "How did we get a block that's being checked from a free list?");
  			break;
  		case BLOCK_STATE_NEED_SWEEPING:
  			if (sweep_block (block))
  				++stat_major_blocks_lazy_swept;
  			break;
  		case BLOCK_STATE_SWEEPING:
  			/* FIXME: do this more elegantly */
  			g_usleep (100);
  			goto retry;
  		default:
  			SGEN_ASSERT (0, FALSE, "Illegal block state");
  			break;
  		}
  	}
  }
  
  static void*
  unlink_slot_from_free_list_uncontested (MSBlockInfo * volatile *free_blocks, int size_index)
  {
  	MSBlockInfo *block, *next_free_block;
  	void *obj, *next_free_slot;
  
   retry:
  	block = free_blocks [size_index];
  	SGEN_ASSERT (9, block, "no free block to unlink from free_blocks %p size_index %d", free_blocks, size_index);
  
  	ensure_can_access_block_free_list (block);
  
  	obj = block->free_list;
  	SGEN_ASSERT (6, obj, "block %p in free list had no available object to alloc from", block);
  
  	next_free_slot = *(void**)obj;
  	if (next_free_slot) {
  		block->free_list = next_free_slot;
  		return obj;
  	}
  
  	next_free_block = block->next_free;
  	if (SGEN_CAS_PTR ((gpointer)&free_blocks [size_index], next_free_block, block) != block)
  		goto retry;
  
  	block->free_list = NULL;
  	block->next_free = NULL;
  
  	return obj;
  }
  
  static GCObject*
  alloc_obj (GCVTable vtable, size_t size, gboolean pinned, gboolean has_references)
  {
  	int size_index = MS_BLOCK_OBJ_SIZE_INDEX (size);
  	MSBlockInfo * volatile * free_blocks = FREE_BLOCKS (pinned, has_references);
  	void *obj;
  
  	if (!free_blocks [size_index]) {
  		if (G_UNLIKELY (!ms_alloc_block (size_index, pinned, has_references)))
  			return NULL;
  	}
  
  	obj = unlink_slot_from_free_list_uncontested (free_blocks, size_index);
  
  	/* FIXME: assumes object layout */
  	*(GCVTable*)obj = vtable;
  
  	return obj;
  }
  
  static GCObject*
  major_alloc_object (GCVTable vtable, size_t size, gboolean has_references)
  {
  	return alloc_obj (vtable, size, FALSE, has_references);
  }
  
  /*
   * We're not freeing the block if it's empty.  We leave that work for
   * the next major collection.
   *
   * This is just called from the domain clearing code, which runs in a
   * single thread and has the GC lock, so we don't need an extra lock.
   */
  static void
  free_object (GCObject *obj, size_t size, gboolean pinned)
  {
  	MSBlockInfo *block = MS_BLOCK_FOR_OBJ (obj);
  	int word, bit;
  	gboolean in_free_list;
  
  	SGEN_ASSERT (9, sweep_state == SWEEP_STATE_SWEPT, "Should have waited for sweep to free objects.");
  
  	ensure_can_access_block_free_list (block);
  	SGEN_ASSERT (9, (pinned && block->pinned) || (!pinned && !block->pinned), "free-object pinning mixup object %p pinned %d block %p pinned %d", obj, pinned, block, block->pinned);
  	SGEN_ASSERT (9, MS_OBJ_ALLOCED (obj, block), "object %p is already free", obj);
  	MS_CALC_MARK_BIT (word, bit, obj);
  	SGEN_ASSERT (9, !MS_MARK_BIT (block, word, bit), "object %p has mark bit set", obj);
  
  	memset (obj, 0, size);
  
  	in_free_list = !!block->free_list;
  	*(void**)obj = block->free_list;
  	block->free_list = (void**)obj;
  
  	if (!in_free_list) {
  		MSBlockInfo * volatile *free_blocks = FREE_BLOCKS (pinned, block->has_references);
  		int size_index = MS_BLOCK_OBJ_SIZE_INDEX (size);
  		SGEN_ASSERT (9, !block->next_free, "block %p doesn't have a free-list of object but belongs to a free-list of blocks", block);
  		add_free_block (free_blocks, size_index, block);
  	}
  }
  
  static void
  major_free_non_pinned_object (GCObject *obj, size_t size)
  {
  	free_object (obj, size, FALSE);
  }
  
  /* size is a multiple of SGEN_ALLOC_ALIGN */
  static GCObject*
  major_alloc_small_pinned_obj (GCVTable vtable, size_t size, gboolean has_references)
  {
  	void *res;
  
  	res = alloc_obj (vtable, size, TRUE, has_references);
  	 /*If we failed to alloc memory, we better try releasing memory
  	  *as pinned alloc is requested by the runtime.
  	  */
  	 if (!res) {
  		sgen_perform_collection (0, GENERATION_OLD, "pinned alloc failure", TRUE);
  		res = alloc_obj (vtable, size, TRUE, has_references);
  	 }
  	 return res;
  }
  
  static void
  free_pinned_object (GCObject *obj, size_t size)
  {
  	free_object (obj, size, TRUE);
  }
  
  /*
   * size is already rounded up and we hold the GC lock.
   */
  static GCObject*
  major_alloc_degraded (GCVTable vtable, size_t size)
  {
  	GCObject *obj;
  
  	obj = alloc_obj (vtable, size, FALSE, SGEN_VTABLE_HAS_REFERENCES (vtable));
  	if (G_LIKELY (obj)) {
  		HEAVY_STAT (++stat_objects_alloced_degraded);
  		HEAVY_STAT (stat_bytes_alloced_degraded += size);
  	}
  	return obj;
  }
  
  /*
   * obj is some object.  If it's not in the major heap (i.e. if it's in
   * the nursery or LOS), return FALSE.  Otherwise return whether it's
   * been marked or copied.
   */
  static gboolean
  major_is_object_live (GCObject *obj)
  {
  	MSBlockInfo *block;
  	int word, bit;
  	mword objsize;
  
  	if (sgen_ptr_in_nursery (obj))
  		return FALSE;
  
  	objsize = SGEN_ALIGN_UP (sgen_safe_object_get_size (obj));
  
  	/* LOS */
  	if (objsize > SGEN_MAX_SMALL_OBJ_SIZE)
  		return FALSE;
  
  	/* now we know it's in a major block */
  	block = MS_BLOCK_FOR_OBJ (obj);
  	SGEN_ASSERT (9, !block->pinned, "block %p is pinned, BTW why is this bad?", block);
  	MS_CALC_MARK_BIT (word, bit, obj);
  	return MS_MARK_BIT (block, word, bit) ? TRUE : FALSE;
  }
  
  static gboolean
  major_ptr_is_in_non_pinned_space (char *ptr, char **start)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		if (ptr >= MS_BLOCK_FOR_BLOCK_INFO (block) && ptr <= MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE) {
  			int count = MS_BLOCK_FREE / block->obj_size;
  			int i;
  
  			*start = NULL;
  			for (i = 0; i <= count; ++i) {
  				if (ptr >= (char*)MS_BLOCK_OBJ (block, i) && ptr < (char*)MS_BLOCK_OBJ (block, i + 1)) {
  					*start = MS_BLOCK_OBJ (block, i);
  					break;
  				}
  			}
  			return !block->pinned;
  		}
  	} END_FOREACH_BLOCK_NO_LOCK;
  	return FALSE;
  }
  
  static gboolean
  try_set_sweep_state (int new, int expected)
  {
  	int old = SGEN_CAS (&sweep_state, new, expected);
  	return old == expected;
  }
  
  static void
  set_sweep_state (int new, int expected)
  {
  	gboolean success = try_set_sweep_state (new, expected);
  	SGEN_ASSERT (0, success, "Could not set sweep state.");
  }
  
  static gboolean ensure_block_is_checked_for_sweeping (int block_index, gboolean wait, gboolean *have_checked);
  
  static SgenThreadPoolJob * volatile sweep_job;
  
  static void
  major_finish_sweep_checking (void)
  {
  	int block_index;
  	SgenThreadPoolJob *job;
  
   retry:
  	switch (sweep_state) {
  	case SWEEP_STATE_SWEPT:
  	case SWEEP_STATE_NEED_SWEEPING:
  		return;
  	case SWEEP_STATE_SWEEPING:
  		if (try_set_sweep_state (SWEEP_STATE_SWEEPING_AND_ITERATING, SWEEP_STATE_SWEEPING))
  			break;
  		goto retry;
  	case SWEEP_STATE_SWEEPING_AND_ITERATING:
  		SGEN_ASSERT (0, FALSE, "Is there another minor collection running?");
  		goto retry;
  	case SWEEP_STATE_COMPACTING:
  		goto wait;
  	default:
  		SGEN_ASSERT (0, FALSE, "Invalid sweep state.");
  		break;
  	}
  
  	/*
  	 * We're running with the world stopped and the only other thread doing work is the
  	 * sweep thread, which doesn't add blocks to the array, so we can safely access
  	 * `next_slot`.
  	 */
  	for (block_index = 0; block_index < allocated_blocks.next_slot; ++block_index)
  		ensure_block_is_checked_for_sweeping (block_index, FALSE, NULL);
  
  	set_sweep_state (SWEEP_STATE_SWEEPING, SWEEP_STATE_SWEEPING_AND_ITERATING);
  
   wait:
  	job = sweep_job;
  	if (job)
  		sgen_thread_pool_job_wait (job);
  	SGEN_ASSERT (0, !sweep_job, "Why did the sweep job not null itself?");
  	SGEN_ASSERT (0, sweep_state == SWEEP_STATE_SWEPT, "How is the sweep job done but we're not swept?");
  }
  
  static void
  major_iterate_objects (IterateObjectsFlags flags, IterateObjectCallbackFunc callback, void *data)
  {
  	gboolean sweep = flags & ITERATE_OBJECTS_SWEEP;
  	gboolean non_pinned = flags & ITERATE_OBJECTS_NON_PINNED;
  	gboolean pinned = flags & ITERATE_OBJECTS_PINNED;
  	MSBlockInfo *block;
  
  	major_finish_sweep_checking ();
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int count = MS_BLOCK_FREE / block->obj_size;
  		int i;
  
  		if (block->pinned && !pinned)
  			continue;
  		if (!block->pinned && !non_pinned)
  			continue;
  		if (sweep && lazy_sweep) {
  			sweep_block (block);
  			SGEN_ASSERT (6, block->state == BLOCK_STATE_SWEPT, "Block must be swept after sweeping");
  		}
  
  		for (i = 0; i < count; ++i) {
  			void **obj = (void**) MS_BLOCK_OBJ (block, i);
  			/*
  			 * We've finished sweep checking, but if we're sweeping lazily and
  			 * the flags don't require us to sweep, the block might still need
  			 * sweeping.  In that case, we need to consult the mark bits to tell
  			 * us whether an object slot is live.
  			 */
  			if (!block_is_swept_or_marking (block)) {
  				int word, bit;
  				SGEN_ASSERT (6, !sweep && block->state == BLOCK_STATE_NEED_SWEEPING, "Has sweeping not finished?");
  				MS_CALC_MARK_BIT (word, bit, obj);
  				if (!MS_MARK_BIT (block, word, bit))
  					continue;
  			}
  			if (MS_OBJ_ALLOCED (obj, block))
  				callback ((GCObject*)obj, block->obj_size, data);
  		}
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  static gboolean
  major_is_valid_object (char *object)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int idx;
  		char *obj;
  
  		if ((MS_BLOCK_FOR_BLOCK_INFO (block) > object) || ((MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE) <= object))
  			continue;
  
  		idx = MS_BLOCK_OBJ_INDEX (object, block);
  		obj = (char*)MS_BLOCK_OBJ (block, idx);
  		if (obj != object)
  			return FALSE;
  		return MS_OBJ_ALLOCED (obj, block);
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	return FALSE;
  }
  
  
  static GCVTable
  major_describe_pointer (char *ptr)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int idx;
  		char *obj;
  		gboolean live;
  		GCVTable vtable;
  		int w, b;
  		gboolean marked;
  
  		if ((MS_BLOCK_FOR_BLOCK_INFO (block) > ptr) || ((MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE) <= ptr))
  			continue;
  
  		SGEN_LOG (0, "major-ptr (block %p sz %d pin %d ref %d)\n",
  			MS_BLOCK_FOR_BLOCK_INFO (block), block->obj_size, block->pinned, block->has_references);
  
  		idx = MS_BLOCK_OBJ_INDEX (ptr, block);
  		obj = (char*)MS_BLOCK_OBJ (block, idx);
  		live = MS_OBJ_ALLOCED (obj, block);
  		vtable = live ? SGEN_LOAD_VTABLE ((GCObject*)obj) : NULL;
  
  		MS_CALC_MARK_BIT (w, b, obj);
  		marked = MS_MARK_BIT (block, w, b);
  
  		if (obj == ptr) {
  			SGEN_LOG (0, "\t(");
  			if (live)
  				SGEN_LOG (0, "object");
  			else
  				SGEN_LOG (0, "dead-object");
  		} else {
  			if (live)
  				SGEN_LOG (0, "interior-ptr offset %zd", ptr - obj);
  			else
  				SGEN_LOG (0, "dead-interior-ptr offset %zd", ptr - obj);
  		}
  
  		SGEN_LOG (0, " marked %d)\n", marked ? 1 : 0);
  
  		return vtable;
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	return NULL;
  }
  
  static void
  major_check_scan_starts (void)
  {
  }
  
  static void
  major_dump_heap (FILE *heap_dump_file)
  {
  	MSBlockInfo *block;
  	int *slots_available = alloca (sizeof (int) * num_block_obj_sizes);
  	int *slots_used = alloca (sizeof (int) * num_block_obj_sizes);
  	int i;
  
  	for (i = 0; i < num_block_obj_sizes; ++i)
  		slots_available [i] = slots_used [i] = 0;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int index = ms_find_block_obj_size_index (block->obj_size);
  		int count = MS_BLOCK_FREE / block->obj_size;
  
  		slots_available [index] += count;
  		for (i = 0; i < count; ++i) {
  			if (MS_OBJ_ALLOCED (MS_BLOCK_OBJ (block, i), block))
  				++slots_used [index];
  		}
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	fprintf (heap_dump_file, "<occupancies>\n");
  	for (i = 0; i < num_block_obj_sizes; ++i) {
  		fprintf (heap_dump_file, "<occupancy size=\"%d\" available=\"%d\" used=\"%d\" />\n",
  				block_obj_sizes [i], slots_available [i], slots_used [i]);
  	}
  	fprintf (heap_dump_file, "</occupancies>\n");
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		int count = MS_BLOCK_FREE / block->obj_size;
  		int i;
  		int start = -1;
  
  		fprintf (heap_dump_file, "<section type=\"%s\" size=\"%zu\">\n", "old", (size_t)MS_BLOCK_FREE);
  
  		for (i = 0; i <= count; ++i) {
  			if ((i < count) && MS_OBJ_ALLOCED (MS_BLOCK_OBJ (block, i), block)) {
  				if (start < 0)
  					start = i;
  			} else {
  				if (start >= 0) {
  					sgen_dump_occupied (MS_BLOCK_OBJ (block, start), MS_BLOCK_OBJ (block, i), MS_BLOCK_FOR_BLOCK_INFO (block));
  					start = -1;
  				}
  			}
  		}
  
  		fprintf (heap_dump_file, "</section>\n");
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  static guint8*
  get_cardtable_mod_union_for_block (MSBlockInfo *block, gboolean allocate)
  {
  	guint8 *mod_union = block->cardtable_mod_union;
  	guint8 *other;
  	if (mod_union)
  		return mod_union;
  	else if (!allocate)
  		return NULL;
  	mod_union = sgen_card_table_alloc_mod_union (MS_BLOCK_FOR_BLOCK_INFO (block), MS_BLOCK_SIZE);
  	other = SGEN_CAS_PTR ((gpointer*)&block->cardtable_mod_union, mod_union, NULL);
  	if (!other) {
  		SGEN_ASSERT (0, block->cardtable_mod_union == mod_union, "Why did CAS not replace?");
  		return mod_union;
  	}
  	sgen_card_table_free_mod_union (mod_union, MS_BLOCK_FOR_BLOCK_INFO (block), MS_BLOCK_SIZE);
  	return other;
  }
  
  static inline guint8*
  major_get_cardtable_mod_union_for_reference (char *ptr)
  {
  	MSBlockInfo *block = MS_BLOCK_FOR_OBJ (ptr);
  	size_t offset = sgen_card_table_get_card_offset (ptr, (char*)sgen_card_table_align_pointer (MS_BLOCK_FOR_BLOCK_INFO (block)));
  	guint8 *mod_union = get_cardtable_mod_union_for_block (block, TRUE);
  	SGEN_ASSERT (0, mod_union, "FIXME: optionally allocate the mod union if it's not here and CAS it in.");
  	return &mod_union [offset];
  }
  
  /*
   * Mark the mod-union card for `ptr`, which must be a reference within the object `obj`.
   */
  static void
  mark_mod_union_card (GCObject *obj, void **ptr)
  {
  	int type = sgen_obj_get_descriptor (obj) & DESC_TYPE_MASK;
  	if (sgen_safe_object_is_small (obj, type)) {
  		guint8 *card_byte = major_get_cardtable_mod_union_for_reference ((char*)ptr);
  		SGEN_ASSERT (0, MS_BLOCK_FOR_OBJ (obj) == MS_BLOCK_FOR_OBJ (ptr), "How can an object and a reference inside it not be in the same block?");
  		*card_byte = 1;
  	} else {
  		sgen_los_mark_mod_union_card (obj, ptr);
  	}
  }
  
  #define LOAD_VTABLE	SGEN_LOAD_VTABLE
  
  #define MS_MARK_OBJECT_AND_ENQUEUE_CHECKED(obj,desc,block,queue) do {	\
  		int __word, __bit;					\
  		MS_CALC_MARK_BIT (__word, __bit, (obj));		\
  		if (!MS_MARK_BIT ((block), __word, __bit) && MS_OBJ_ALLOCED ((obj), (block))) {	\
  			MS_SET_MARK_BIT ((block), __word, __bit);	\
  			if (sgen_gc_descr_has_references (desc))			\
  				GRAY_OBJECT_ENQUEUE ((queue), (obj), (desc)); \
  			binary_protocol_mark ((obj), (gpointer)LOAD_VTABLE ((obj)), sgen_safe_object_get_size ((obj))); \
  			INC_NUM_MAJOR_OBJECTS_MARKED ();		\
  		}							\
  	} while (0)
  #define MS_MARK_OBJECT_AND_ENQUEUE(obj,desc,block,queue) do {		\
  		int __word, __bit;					\
  		MS_CALC_MARK_BIT (__word, __bit, (obj));		\
  		SGEN_ASSERT (9, MS_OBJ_ALLOCED ((obj), (block)), "object %p not allocated", obj); \
  		if (!MS_MARK_BIT ((block), __word, __bit)) {		\
  			MS_SET_MARK_BIT ((block), __word, __bit);	\
  			if (sgen_gc_descr_has_references (desc))			\
  				GRAY_OBJECT_ENQUEUE ((queue), (obj), (desc)); \
  			binary_protocol_mark ((obj), (gpointer)LOAD_VTABLE ((obj)), sgen_safe_object_get_size ((obj))); \
  			INC_NUM_MAJOR_OBJECTS_MARKED ();		\
  		}							\
  	} while (0)
  
  static void
  pin_major_object (GCObject *obj, SgenGrayQueue *queue)
  {
  	MSBlockInfo *block;
  
  	if (concurrent_mark)
  		g_assert_not_reached ();
  
  	block = MS_BLOCK_FOR_OBJ (obj);
  	block->has_pinned = TRUE;
  	MS_MARK_OBJECT_AND_ENQUEUE (obj, sgen_obj_get_descriptor (obj), block, queue);
  }
  
  #include "sgen-major-copy-object.h"
  
  static long long
  major_get_and_reset_num_major_objects_marked (void)
  {
  #ifdef SGEN_COUNT_NUMBER_OF_MAJOR_OBJECTS_MARKED
  	long long num = num_major_objects_marked;
  	num_major_objects_marked = 0;
  	return num;
  #else
  	return 0;
  #endif
  }
  
  #define PREFETCH_CARDS		1	/* BOOL FASTENABLE */
  #if !PREFETCH_CARDS
  #undef PREFETCH_CARDS
  #endif
  
  /* gcc 4.2.1 from xcode4 crashes on sgen_card_table_get_card_address () when this is enabled */
  #if defined(PLATFORM_MACOSX)
  #define GCC_VERSION (__GNUC__ * 10000 \
                                 + __GNUC_MINOR__ * 100 \
                                 + __GNUC_PATCHLEVEL__)
  #if GCC_VERSION <= 40300
  #undef PREFETCH_CARDS
  #endif
  #endif
  
  #ifdef HEAVY_STATISTICS
  static guint64 stat_optimized_copy;
  static guint64 stat_optimized_copy_nursery;
  static guint64 stat_optimized_copy_nursery_forwarded;
  static guint64 stat_optimized_copy_nursery_pinned;
  static guint64 stat_optimized_copy_major;
  static guint64 stat_optimized_copy_major_small_fast;
  static guint64 stat_optimized_copy_major_small_slow;
  static guint64 stat_optimized_copy_major_large;
  static guint64 stat_optimized_copy_major_forwarded;
  static guint64 stat_optimized_copy_major_small_evacuate;
  static guint64 stat_optimized_major_scan;
  static guint64 stat_optimized_major_scan_no_refs;
  
  static guint64 stat_drain_prefetch_fills;
  static guint64 stat_drain_prefetch_fill_failures;
  static guint64 stat_drain_loops;
  #endif
  
  static void major_scan_object_with_evacuation (GCObject *start, mword desc, SgenGrayQueue *queue);
  
  #define COPY_OR_MARK_FUNCTION_NAME	major_copy_or_mark_object_no_evacuation
  #define SCAN_OBJECT_FUNCTION_NAME	major_scan_object_no_evacuation
  #define DRAIN_GRAY_STACK_FUNCTION_NAME	drain_gray_stack_no_evacuation
  #include "sgen-marksweep-drain-gray-stack.h"
  
  #define COPY_OR_MARK_WITH_EVACUATION
  #define COPY_OR_MARK_FUNCTION_NAME	major_copy_or_mark_object_with_evacuation
  #define SCAN_OBJECT_FUNCTION_NAME	major_scan_object_with_evacuation
  #define DRAIN_GRAY_STACK_FUNCTION_NAME	drain_gray_stack_with_evacuation
  #include "sgen-marksweep-drain-gray-stack.h"
  
  #undef COPY_OR_MARK_WITH_EVACUATION
  #define COPY_OR_MARK_CONCURRENT
  #define COPY_OR_MARK_FUNCTION_NAME	major_copy_or_mark_object_concurrent
  #define SCAN_OBJECT_FUNCTION_NAME	major_scan_object_concurrent
  #define DRAIN_GRAY_STACK_FUNCTION_NAME	drain_gray_stack_concurrent
  #include "sgen-marksweep-drain-gray-stack.h"
  
  static gboolean
  drain_gray_stack (SgenGrayQueue *queue)
  {
  	gboolean evacuation = FALSE;
  	int i;
  	for (i = 0; i < num_block_obj_sizes; ++i) {
  		if (evacuate_block_obj_sizes [i]) {
  			evacuation = TRUE;
  			break;
  		}
  	}
  
  	if (evacuation)
  		return drain_gray_stack_with_evacuation (queue);
  	else
  		return drain_gray_stack_no_evacuation (queue);
  }
  
  #include "sgen-marksweep-scan-object-concurrent.h"
  
  static void
  major_copy_or_mark_object_canonical (GCObject **ptr, SgenGrayQueue *queue)
  {
  	major_copy_or_mark_object_with_evacuation (ptr, *ptr, queue);
  }
  
  static void
  major_copy_or_mark_object_concurrent_canonical (GCObject **ptr, SgenGrayQueue *queue)
  {
  	major_copy_or_mark_object_concurrent (ptr, *ptr, queue);
  }
  
  static void
  major_copy_or_mark_object_concurrent_finish_canonical (GCObject **ptr, SgenGrayQueue *queue)
  {
  	major_copy_or_mark_object_no_evacuation (ptr, *ptr, queue);
  }
  
  static void
  mark_pinned_objects_in_block (MSBlockInfo *block, size_t first_entry, size_t last_entry, SgenGrayQueue *queue)
  {
  	void **entry, **end;
  	int last_index = -1;
  
  	if (first_entry == last_entry)
  		return;
  
  	block->has_pinned = TRUE;
  
  	entry = sgen_pinning_get_entry (first_entry);
  	end = sgen_pinning_get_entry (last_entry);
  
  	for (; entry < end; ++entry) {
  		int index = MS_BLOCK_OBJ_INDEX (*entry, block);
  		GCObject *obj;
  		SGEN_ASSERT (9, index >= 0 && index < MS_BLOCK_FREE / block->obj_size, "invalid object %p index %d max-index %d", *entry, index, (int)(MS_BLOCK_FREE / block->obj_size));
  		if (index == last_index)
  			continue;
  		obj = MS_BLOCK_OBJ (block, index);
  		MS_MARK_OBJECT_AND_ENQUEUE_CHECKED (obj, sgen_obj_get_descriptor (obj), block, queue);
  		last_index = index;
  	}
  }
  
  static inline void
  sweep_block_for_size (MSBlockInfo *block, int count, int obj_size)
  {
  	int obj_index;
  
  	for (obj_index = 0; obj_index < count; ++obj_index) {
  		int word, bit;
  		void *obj = MS_BLOCK_OBJ_FOR_SIZE (block, obj_index, obj_size);
  
  		MS_CALC_MARK_BIT (word, bit, obj);
  		if (MS_MARK_BIT (block, word, bit)) {
  			SGEN_ASSERT (9, MS_OBJ_ALLOCED (obj, block), "object %p not allocated", obj);
  		} else {
  			/* an unmarked object */
  			if (MS_OBJ_ALLOCED (obj, block)) {
  				/*
  				 * FIXME: Merge consecutive
  				 * slots for lower reporting
  				 * overhead.  Maybe memset
  				 * will also benefit?
  				 */
  				binary_protocol_empty (obj, obj_size);
  				memset (obj, 0, obj_size);
  			}
  			*(void**)obj = block->free_list;
  			block->free_list = obj;
  		}
  	}
  }
  
  static inline gboolean
  try_set_block_state (MSBlockInfo *block, gint32 new_state, gint32 expected_state)
  {
  	gint32 old_state = SGEN_CAS (&block->state, new_state, expected_state);
  	gboolean success = old_state == expected_state;
  	if (success)
  		binary_protocol_block_set_state (block, MS_BLOCK_SIZE, old_state, new_state);
  	return success;
  }
  
  static inline void
  set_block_state (MSBlockInfo *block, gint32 new_state, gint32 expected_state)
  {
  	SGEN_ASSERT (6, block->state == expected_state, "Block state incorrect before set");
  	block->state = new_state;
  }
  
  /*
   * If `block` needs sweeping, sweep it and return TRUE.  Otherwise return FALSE.
   *
   * Sweeping means iterating through the block's slots and building the free-list from the
   * unmarked ones.  They will also be zeroed.  The mark bits will be reset.
   */
  static gboolean
  sweep_block (MSBlockInfo *block)
  {
  	int count;
  	void *reversed = NULL;
  
   retry:
  	switch (block->state) {
  	case BLOCK_STATE_SWEPT:
  		return FALSE;
  	case BLOCK_STATE_MARKING:
  	case BLOCK_STATE_CHECKING:
  		SGEN_ASSERT (0, FALSE, "How did we get to sweep a block that's being marked or being checked?");
  		goto retry;
  	case BLOCK_STATE_SWEEPING:
  		/* FIXME: Do this more elegantly */
  		g_usleep (100);
  		goto retry;
  	case BLOCK_STATE_NEED_SWEEPING:
  		if (!try_set_block_state (block, BLOCK_STATE_SWEEPING, BLOCK_STATE_NEED_SWEEPING))
  			goto retry;
  		break;
  	default:
  		SGEN_ASSERT (0, FALSE, "Illegal block state");
  	}
  
  	SGEN_ASSERT (6, block->state == BLOCK_STATE_SWEEPING, "How did we get here without setting state to sweeping?");
  
  	count = MS_BLOCK_FREE / block->obj_size;
  
  	block->free_list = NULL;
  
  	/* Use inline instances specialized to constant sizes, this allows the compiler to replace the memset calls with inline code */
  	// FIXME: Add more sizes
  	switch (block->obj_size) {
  	case 16:
  		sweep_block_for_size (block, count, 16);
  		break;
  	default:
  		sweep_block_for_size (block, count, block->obj_size);
  		break;
  	}
  
  	/* reset mark bits */
  	memset (block->mark_words, 0, sizeof (mword) * MS_NUM_MARK_WORDS);
  
  	/* Reverse free list so that it's in address order */
  	reversed = NULL;
  	while (block->free_list) {
  		void *next = *(void**)block->free_list;
  		*(void**)block->free_list = reversed;
  		reversed = block->free_list;
  		block->free_list = next;
  	}
  	block->free_list = reversed;
  
  	mono_memory_write_barrier ();
  
  	set_block_state (block, BLOCK_STATE_SWEPT, BLOCK_STATE_SWEEPING);
  
  	return TRUE;
  }
  
  static inline int
  bitcount (mword d)
  {
  	int count = 0;
  
  #ifdef __GNUC__
  	if (sizeof (mword) == sizeof (unsigned long))
  		count += __builtin_popcountl (d);
  	else
  		count += __builtin_popcount (d);
  #else
  	while (d) {
  		count ++;
  		d &= (d - 1);
  	}
  #endif
  	return count;
  }
  
  /* statistics for evacuation */
  static size_t *sweep_slots_available;
  static size_t *sweep_slots_used;
  static size_t *sweep_num_blocks;
  
  static volatile size_t num_major_sections_before_sweep;
  static volatile size_t num_major_sections_freed_in_sweep;
  
  static void
  sweep_start (void)
  {
  	int i;
  
  	for (i = 0; i < num_block_obj_sizes; ++i)
  		sweep_slots_available [i] = sweep_slots_used [i] = sweep_num_blocks [i] = 0;
  
  	/* clear all the free lists */
  	for (i = 0; i < MS_BLOCK_TYPE_MAX; ++i) {
  		MSBlockInfo * volatile *free_blocks = free_block_lists [i];
  		int j;
  		for (j = 0; j < num_block_obj_sizes; ++j)
  			free_blocks [j] = NULL;
  	}
  }
  
  static void sweep_finish (void);
  
  /*
   * If `wait` is TRUE and the block is currently being checked, this function will wait until
   * the checking has finished.
   *
   * Returns whether the block is still there.  If `wait` is FALSE, the return value will not
   * be correct, i.e. must not be used.
   */
  static gboolean
  ensure_block_is_checked_for_sweeping (int block_index, gboolean wait, gboolean *have_checked)
  {
  	int count;
  	gboolean have_live = FALSE;
  	gboolean have_free = FALSE;
  	int nused = 0;
  	int block_state;
  	int i;
  	void *tagged_block;
  	MSBlockInfo *block;
  
  	SGEN_ASSERT (6, sweep_in_progress (), "Why do we call this function if there's no sweep in progress?");
  
  	if (have_checked)
  		*have_checked = FALSE;
  
   retry:
  	tagged_block = *(void * volatile *)&allocated_blocks.data [block_index];
  	if (!tagged_block)
  		return FALSE;
  
  	if (BLOCK_IS_TAGGED_CHECKING (tagged_block)) {
  		if (!wait)
  			return FALSE;
  		/* FIXME: do this more elegantly */
  		g_usleep (100);
  		goto retry;
  	}
  
  	if (SGEN_CAS_PTR (&allocated_blocks.data [block_index], BLOCK_TAG_CHECKING (tagged_block), tagged_block) != tagged_block)
  		goto retry;
  
  	block = BLOCK_UNTAG (tagged_block);
  	block_state = block->state;
  
  	if (!sweep_in_progress ()) {
  		SGEN_ASSERT (6, block_state != BLOCK_STATE_SWEEPING && block_state != BLOCK_STATE_CHECKING, "Invalid block state.");
  		if (!lazy_sweep)
  			SGEN_ASSERT (6, block_state != BLOCK_STATE_NEED_SWEEPING, "Invalid block state.");
  	}
  
  	switch (block_state) {
  	case BLOCK_STATE_SWEPT:
  	case BLOCK_STATE_NEED_SWEEPING:
  	case BLOCK_STATE_SWEEPING:
  		goto done;
  	case BLOCK_STATE_MARKING:
  		break;
  	case BLOCK_STATE_CHECKING:
  		SGEN_ASSERT (0, FALSE, "We set the CHECKING bit - how can the stage be CHECKING?");
  		goto done;
  	default:
  		SGEN_ASSERT (0, FALSE, "Illegal block state");
  		break;
  	}
  
  	SGEN_ASSERT (6, block->state == BLOCK_STATE_MARKING, "When we sweep all blocks must start out marking.");
  	set_block_state (block, BLOCK_STATE_CHECKING, BLOCK_STATE_MARKING);
  
  	if (have_checked)
  		*have_checked = TRUE;
  
  	block->has_pinned = block->pinned;
  
  	block->is_to_space = FALSE;
  
  	count = MS_BLOCK_FREE / block->obj_size;
  
  	if (block->cardtable_mod_union) {
  		sgen_card_table_free_mod_union (block->cardtable_mod_union, MS_BLOCK_FOR_BLOCK_INFO (block), MS_BLOCK_SIZE);
  		block->cardtable_mod_union = NULL;
  	}
  
  	/* Count marked objects in the block */
  	for (i = 0; i < MS_NUM_MARK_WORDS; ++i)
  		nused += bitcount (block->mark_words [i]);
  
  	if (nused)
  		have_live = TRUE;
  	if (nused < count)
  		have_free = TRUE;
  
  	if (have_live) {
  		int obj_size_index = block->obj_size_index;
  		gboolean has_pinned = block->has_pinned;
  
  		set_block_state (block, BLOCK_STATE_NEED_SWEEPING, BLOCK_STATE_CHECKING);
  
  		/*
  		 * FIXME: Go straight to SWEPT if there are no free slots.  We need
  		 * to set the free slot list to NULL, though, and maybe update some
  		 * statistics.
  		 */
  		if (!lazy_sweep)
  			sweep_block (block);
  
  		if (!has_pinned) {
  			++sweep_num_blocks [obj_size_index];
  			sweep_slots_used [obj_size_index] += nused;
  			sweep_slots_available [obj_size_index] += count;
  		}
  
  		/*
  		 * If there are free slots in the block, add
  		 * the block to the corresponding free list.
  		 */
  		if (have_free) {
  			MSBlockInfo * volatile *free_blocks = FREE_BLOCKS (block->pinned, block->has_references);
  
  			if (!lazy_sweep)
  				SGEN_ASSERT (6, block->free_list, "How do we not have a free list when there are free slots?");
  
  			add_free_block (free_blocks, obj_size_index, block);
  		}
  
  		/* FIXME: Do we need the heap boundaries while we do nursery collections? */
  		update_heap_boundaries_for_block (block);
  	} else {
  		/*
  		 * Blocks without live objects are removed from the
  		 * block list and freed.
  		 */
  		SGEN_ASSERT (6, block_index < allocated_blocks.next_slot, "How did the number of blocks shrink?");
  		SGEN_ASSERT (6, allocated_blocks.data [block_index] == BLOCK_TAG_CHECKING (tagged_block), "How did the block move?");
  
  		binary_protocol_empty (MS_BLOCK_OBJ (block, 0), (char*)MS_BLOCK_OBJ (block, count) - (char*)MS_BLOCK_OBJ (block, 0));
  		ms_free_block (block);
  
  		SGEN_ATOMIC_ADD_P (num_major_sections, -1);
  
  		tagged_block = NULL;
  	}
  
   done:
  	allocated_blocks.data [block_index] = tagged_block;
  	return !!tagged_block;
  }
  
  static void
  sweep_job_func (void *thread_data_untyped, SgenThreadPoolJob *job)
  {
  	int block_index;
  	int num_blocks = num_major_sections_before_sweep;
  
  	SGEN_ASSERT (0, sweep_in_progress (), "Sweep thread called with wrong state");
  	SGEN_ASSERT (0, num_blocks <= allocated_blocks.next_slot, "How did we lose blocks?");
  
  	/*
  	 * We traverse the block array from high to low.  Nursery collections will have to
  	 * cooperate with the sweep thread to finish sweeping, and they will traverse from
  	 * low to high, to avoid constantly colliding on the same blocks.
  	 */
  	for (block_index = num_blocks - 1; block_index >= 0; --block_index) {
  		gboolean have_checked;
  
  		/*
  		 * The block might have been freed by another thread doing some checking
  		 * work.
  		 */
  		if (!ensure_block_is_checked_for_sweeping (block_index, TRUE, &have_checked))
  			++num_major_sections_freed_in_sweep;
  	}
  
  	while (!try_set_sweep_state (SWEEP_STATE_COMPACTING, SWEEP_STATE_SWEEPING)) {
  		/*
  		 * The main GC thread is currently iterating over the block array to help us
  		 * finish the sweep.  We have already finished, but we don't want to mess up
  		 * that iteration, so we just wait for it.
  		 */
  		g_usleep (100);
  	}
  
  	if (SGEN_MAX_ASSERT_LEVEL >= 6) {
  		for (block_index = num_blocks; block_index < allocated_blocks.next_slot; ++block_index) {
  			MSBlockInfo *block = BLOCK_UNTAG (allocated_blocks.data [block_index]);
  			SGEN_ASSERT (6, block && block->state == BLOCK_STATE_SWEPT, "How did a new block to be swept get added while swept?");
  		}
  	}
  
  	sgen_pointer_queue_remove_nulls (&allocated_blocks);
  	mono_memory_barrier ();
  
  	sweep_finish ();
  
  	sweep_job = NULL;
  }
  
  static void
  sweep_finish (void)
  {
  	mword total_evacuate_heap = 0;
  	mword total_evacuate_saved = 0;
  	int i;
  
  	for (i = 0; i < num_block_obj_sizes; ++i) {
  		float usage = (float)sweep_slots_used [i] / (float)sweep_slots_available [i];
  		if (sweep_num_blocks [i] > 5 && usage < evacuation_threshold) {
  			evacuate_block_obj_sizes [i] = TRUE;
  			/*
  			g_print ("slot size %d - %d of %d used\n",
  					block_obj_sizes [i], slots_used [i], slots_available [i]);
  			*/
  		} else {
  			evacuate_block_obj_sizes [i] = FALSE;
  		}
  		{
  			mword total_bytes = block_obj_sizes [i] * sweep_slots_available [i];
  			total_evacuate_heap += total_bytes;
  			if (evacuate_block_obj_sizes [i])
  				total_evacuate_saved += total_bytes - block_obj_sizes [i] * sweep_slots_used [i];
  		}
  	}
  
  	want_evacuation = (float)total_evacuate_saved / (float)total_evacuate_heap > (1 - concurrent_evacuation_threshold);
  
  	set_sweep_state (SWEEP_STATE_SWEPT, SWEEP_STATE_COMPACTING);
  }
  
  static void
  major_sweep (void)
  {
  	set_sweep_state (SWEEP_STATE_SWEEPING, SWEEP_STATE_NEED_SWEEPING);
  
  	sweep_start ();
  
  	SGEN_ASSERT (0, num_major_sections == allocated_blocks.next_slot, "We don't know how many blocks we have?");
  
  	num_major_sections_before_sweep = num_major_sections;
  	num_major_sections_freed_in_sweep = 0;
  
  	SGEN_ASSERT (0, !sweep_job, "We haven't finished the last sweep?");
  	if (concurrent_sweep) {
  		sweep_job = sgen_thread_pool_job_alloc ("sweep", sweep_job_func, sizeof (SgenThreadPoolJob));
  		sgen_thread_pool_job_enqueue (sweep_job);
  	} else {
  		sweep_job_func (NULL, NULL);
  	}
  }
  
  static gboolean
  major_have_swept (void)
  {
  	return sweep_state == SWEEP_STATE_SWEPT;
  }
  
  static int count_pinned_ref;
  static int count_pinned_nonref;
  static int count_nonpinned_ref;
  static int count_nonpinned_nonref;
  
  static void
  count_nonpinned_callback (GCObject *obj, size_t size, void *data)
  {
  	GCVTable vtable = LOAD_VTABLE (obj);
  
  	if (SGEN_VTABLE_HAS_REFERENCES (vtable))
  		++count_nonpinned_ref;
  	else
  		++count_nonpinned_nonref;
  }
  
  static void
  count_pinned_callback (GCObject *obj, size_t size, void *data)
  {
  	GCVTable vtable = LOAD_VTABLE (obj);
  
  	if (SGEN_VTABLE_HAS_REFERENCES (vtable))
  		++count_pinned_ref;
  	else
  		++count_pinned_nonref;
  }
  
  static G_GNUC_UNUSED void
  count_ref_nonref_objs (void)
  {
  	int total;
  
  	count_pinned_ref = 0;
  	count_pinned_nonref = 0;
  	count_nonpinned_ref = 0;
  	count_nonpinned_nonref = 0;
  
  	major_iterate_objects (ITERATE_OBJECTS_SWEEP_NON_PINNED, count_nonpinned_callback, NULL);
  	major_iterate_objects (ITERATE_OBJECTS_SWEEP_PINNED, count_pinned_callback, NULL);
  
  	total = count_pinned_nonref + count_nonpinned_nonref + count_pinned_ref + count_nonpinned_ref;
  
  	g_print ("ref: %d pinned %d non-pinned   non-ref: %d pinned %d non-pinned  --  %.1f\n",
  			count_pinned_ref, count_nonpinned_ref,
  			count_pinned_nonref, count_nonpinned_nonref,
  			(count_pinned_nonref + count_nonpinned_nonref) * 100.0 / total);
  }
  
  static int
  ms_calculate_block_obj_sizes (double factor, int *arr)
  {
  	double target_size;
  	int num_sizes = 0;
  	int last_size = 0;
  
  	/*
  	 * Have every possible slot size starting with the minimal
  	 * object size up to and including four times that size.  Then
  	 * proceed by increasing geometrically with the given factor.
  	 */
  
  	for (int size = SGEN_CLIENT_MINIMUM_OBJECT_SIZE; size <= 4 * SGEN_CLIENT_MINIMUM_OBJECT_SIZE; size += SGEN_ALLOC_ALIGN) {
  		if (arr)
  			arr [num_sizes] = size;
  		++num_sizes;
  		last_size = size;
  	}
  	target_size = (double)last_size;
  
  	do {
  		int target_count = (int)floor (MS_BLOCK_FREE / target_size);
  		int size = MIN ((MS_BLOCK_FREE / target_count) & ~(SGEN_ALLOC_ALIGN - 1), SGEN_MAX_SMALL_OBJ_SIZE);
  
  		if (size != last_size) {
  			if (arr)
  				arr [num_sizes] = size;
  			++num_sizes;
  			last_size = size;
  		}
  
  		target_size *= factor;
  	} while (last_size < SGEN_MAX_SMALL_OBJ_SIZE);
  
  	return num_sizes;
  }
  
  /* only valid during minor collections */
  static mword old_num_major_sections;
  
  static void
  major_start_nursery_collection (void)
  {
  #ifdef MARKSWEEP_CONSISTENCY_CHECK
  	consistency_check ();
  #endif
  
  	old_num_major_sections = num_major_sections;
  }
  
  static void
  major_finish_nursery_collection (void)
  {
  #ifdef MARKSWEEP_CONSISTENCY_CHECK
  	consistency_check ();
  #endif
  }
  
  static void
  major_start_major_collection (void)
  {
  	MSBlockInfo *block;
  	int i;
  
  	major_finish_sweep_checking ();
  
  	/*
  	 * Clear the free lists for block sizes where we do evacuation.  For those block
  	 * sizes we will have to allocate new blocks.
  	 */
  	for (i = 0; i < num_block_obj_sizes; ++i) {
  		if (!evacuate_block_obj_sizes [i])
  			continue;
  
  		free_block_lists [0][i] = NULL;
  		free_block_lists [MS_BLOCK_FLAG_REFS][i] = NULL;
  	}
  
  	if (lazy_sweep)
  		binary_protocol_sweep_begin (GENERATION_OLD, TRUE);
  
  	/* Sweep all unswept blocks and set them to MARKING */
  	FOREACH_BLOCK_NO_LOCK (block) {
  		if (lazy_sweep)
  			sweep_block (block);
  		SGEN_ASSERT (0, block->state == BLOCK_STATE_SWEPT, "All blocks must be swept when we're pinning.");
  		set_block_state (block, BLOCK_STATE_MARKING, BLOCK_STATE_SWEPT);
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	if (lazy_sweep)
  		binary_protocol_sweep_end (GENERATION_OLD, TRUE);
  
  	set_sweep_state (SWEEP_STATE_NEED_SWEEPING, SWEEP_STATE_SWEPT);
  }
  
  static void
  major_finish_major_collection (ScannedObjectCounts *counts)
  {
  #ifdef SGEN_HEAVY_BINARY_PROTOCOL
  	if (binary_protocol_is_enabled ()) {
  		counts->num_scanned_objects = scanned_objects_list.next_slot;
  
  		sgen_pointer_queue_sort_uniq (&scanned_objects_list);
  		counts->num_unique_scanned_objects = scanned_objects_list.next_slot;
  
  		sgen_pointer_queue_clear (&scanned_objects_list);
  	}
  #endif
  }
  
  #if SIZEOF_VOID_P != 8
  static int
  compare_pointers (const void *va, const void *vb) {
  	char *a = *(char**)va, *b = *(char**)vb;
  	if (a < b)
  		return -1;
  	if (a > b)
  		return 1;
  	return 0;
  }
  #endif
  
  /*
   * This is called with sweep completed and the world stopped.
   */
  static void
  major_free_swept_blocks (size_t allowance)
  {
  	/* FIXME: This is probably too much.  It's assuming all objects are small. */
  	size_t section_reserve = allowance / MS_BLOCK_SIZE;
  
  	SGEN_ASSERT (0, sweep_state == SWEEP_STATE_SWEPT, "Sweeping must have finished before freeing blocks");
  
  #if SIZEOF_VOID_P != 8
  	{
  		int i, num_empty_blocks_orig, num_blocks, arr_length;
  		void *block;
  		void **empty_block_arr;
  		void **rebuild_next;
  
  #ifdef TARGET_WIN32
  		/*
  		 * sgen_free_os_memory () asserts in mono_vfree () because windows doesn't like freeing the middle of
  		 * a VirtualAlloc ()-ed block.
  		 */
  		return;
  #endif
  
  		if (num_empty_blocks <= section_reserve)
  			return;
  		SGEN_ASSERT (0, num_empty_blocks > 0, "section reserve can't be negative");
  
  		num_empty_blocks_orig = num_empty_blocks;
  		empty_block_arr = (void**)sgen_alloc_internal_dynamic (sizeof (void*) * num_empty_blocks_orig,
  				INTERNAL_MEM_MS_BLOCK_INFO_SORT, FALSE);
  		if (!empty_block_arr)
  			goto fallback;
  
  		i = 0;
  		for (block = empty_blocks; block; block = *(void**)block)
  			empty_block_arr [i++] = block;
  		SGEN_ASSERT (0, i == num_empty_blocks, "empty block count wrong");
  
  		sgen_qsort (empty_block_arr, num_empty_blocks, sizeof (void*), compare_pointers);
  
  		/*
  		 * We iterate over the free blocks, trying to find MS_BLOCK_ALLOC_NUM
  		 * contiguous ones.  If we do, we free them.  If that's not enough to get to
  		 * section_reserve, we halve the number of contiguous blocks we're looking
  		 * for and have another go, until we're done with looking for pairs of
  		 * blocks, at which point we give up and go to the fallback.
  		 */
  		arr_length = num_empty_blocks_orig;
  		num_blocks = MS_BLOCK_ALLOC_NUM;
  		while (num_empty_blocks > section_reserve && num_blocks > 1) {
  			int first = -1;
  			int dest = 0;
  
  			dest = 0;
  			for (i = 0; i < arr_length; ++i) {
  				int d = dest;
  				void *block = empty_block_arr [i];
  				SGEN_ASSERT (6, block, "we're not shifting correctly");
  				if (i != dest) {
  					empty_block_arr [dest] = block;
  					/*
  					 * This is not strictly necessary, but we're
  					 * cautious.
  					 */
  					empty_block_arr [i] = NULL;
  				}
  				++dest;
  
  				if (first < 0) {
  					first = d;
  					continue;
  				}
  
  				SGEN_ASSERT (6, first >= 0 && d > first, "algorithm is wrong");
  
  				if ((char*)block != ((char*)empty_block_arr [d-1]) + MS_BLOCK_SIZE) {
  					first = d;
  					continue;
  				}
  
  				if (d + 1 - first == num_blocks) {
  					/*
  					 * We found num_blocks contiguous blocks.  Free them
  					 * and null their array entries.  As an optimization
  					 * we could, instead of nulling the entries, shift
  					 * the following entries over to the left, while
  					 * we're iterating.
  					 */
  					int j;
  					sgen_free_os_memory (empty_block_arr [first], MS_BLOCK_SIZE * num_blocks, SGEN_ALLOC_HEAP);
  					for (j = first; j <= d; ++j)
  						empty_block_arr [j] = NULL;
  					dest = first;
  					first = -1;
  
  					num_empty_blocks -= num_blocks;
  
  					stat_major_blocks_freed += num_blocks;
  					if (num_blocks == MS_BLOCK_ALLOC_NUM)
  						stat_major_blocks_freed_ideal += num_blocks;
  					else
  						stat_major_blocks_freed_less_ideal += num_blocks;
  
  				}
  			}
  
  			SGEN_ASSERT (6, dest <= i && dest <= arr_length, "array length is off");
  			arr_length = dest;
  			SGEN_ASSERT (6, arr_length == num_empty_blocks, "array length is off");
  
  			num_blocks >>= 1;
  		}
  
  		/* rebuild empty_blocks free list */
  		rebuild_next = (void**)&empty_blocks;
  		for (i = 0; i < arr_length; ++i) {
  			void *block = empty_block_arr [i];
  			SGEN_ASSERT (6, block, "we're missing blocks");
  			*rebuild_next = block;
  			rebuild_next = (void**)block;
  		}
  		*rebuild_next = NULL;
  
  		/* free array */
  		sgen_free_internal_dynamic (empty_block_arr, sizeof (void*) * num_empty_blocks_orig, INTERNAL_MEM_MS_BLOCK_INFO_SORT);
  	}
  
  	SGEN_ASSERT (0, num_empty_blocks >= 0, "we freed more blocks than we had in the first place?");
  
   fallback:
  	/*
  	 * This is our threshold.  If there's not more empty than used blocks, we won't
  	 * release uncontiguous blocks, in fear of fragmenting the address space.
  	 */
  	if (num_empty_blocks <= num_major_sections)
  		return;
  #endif
  
  	while (num_empty_blocks > section_reserve) {
  		void *next = *(void**)empty_blocks;
  		sgen_free_os_memory (empty_blocks, MS_BLOCK_SIZE, SGEN_ALLOC_HEAP);
  		empty_blocks = next;
  		/*
  		 * Needs not be atomic because this is running
  		 * single-threaded.
  		 */
  		--num_empty_blocks;
  
  		++stat_major_blocks_freed;
  #if SIZEOF_VOID_P != 8
  		++stat_major_blocks_freed_individual;
  #endif
  	}
  }
  
  static void
  major_pin_objects (SgenGrayQueue *queue)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		size_t first_entry, last_entry;
  		SGEN_ASSERT (6, block_is_swept_or_marking (block), "All blocks must be swept when we're pinning.");
  		sgen_find_optimized_pin_queue_area (MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SKIP, MS_BLOCK_FOR_BLOCK_INFO (block) + MS_BLOCK_SIZE,
  				&first_entry, &last_entry);
  		mark_pinned_objects_in_block (block, first_entry, last_entry, queue);
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  static void
  major_init_to_space (void)
  {
  }
  
  static void
  major_report_pinned_memory_usage (void)
  {
  	g_assert_not_reached ();
  }
  
  static gint64
  major_get_used_size (void)
  {
  	gint64 size = 0;
  	MSBlockInfo *block;
  
  	/*
  	 * We're holding the GC lock, but the sweep thread might be running.  Make sure it's
  	 * finished, then we can iterate over the block array.
  	 */
  	major_finish_sweep_checking ();
  
  	FOREACH_BLOCK_NO_LOCK_CONDITION (TRUE, block) {
  		int count = MS_BLOCK_FREE / block->obj_size;
  		void **iter;
  		size += count * block->obj_size;
  		for (iter = block->free_list; iter; iter = (void**)*iter)
  			size -= block->obj_size;
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	return size;
  }
  
  /* FIXME: return number of bytes, not of sections */
  static size_t
  get_num_major_sections (void)
  {
  	return num_major_sections;
  }
  
  /*
   * Returns the number of bytes in blocks that were present when the last sweep was
   * initiated, and were not freed during the sweep.  They are the basis for calculating the
   * allowance.
   */
  static size_t
  get_bytes_survived_last_sweep (void)
  {
  	SGEN_ASSERT (0, sweep_state == SWEEP_STATE_SWEPT, "Can only query unswept sections after sweep");
  	return (num_major_sections_before_sweep - num_major_sections_freed_in_sweep) * MS_BLOCK_SIZE;
  }
  
  static gboolean
  major_handle_gc_param (const char *opt)
  {
  	if (g_str_has_prefix (opt, "evacuation-threshold=")) {
  		const char *arg = strchr (opt, '=') + 1;
  		int percentage = atoi (arg);
  		if (percentage < 0 || percentage > 100) {
  			fprintf (stderr, "evacuation-threshold must be an integer in the range 0-100.\n");
  			exit (1);
  		}
  		evacuation_threshold = (float)percentage / 100.0f;
  		return TRUE;
  	} else if (!strcmp (opt, "lazy-sweep")) {
  		lazy_sweep = TRUE;
  		return TRUE;
  	} else if (!strcmp (opt, "no-lazy-sweep")) {
  		lazy_sweep = FALSE;
  		return TRUE;
  	} else if (!strcmp (opt, "concurrent-sweep")) {
  		concurrent_sweep = TRUE;
  		return TRUE;
  	} else if (!strcmp (opt, "no-concurrent-sweep")) {
  		concurrent_sweep = FALSE;
  		return TRUE;
  	}
  
  	return FALSE;
  }
  
  static void
  major_print_gc_param_usage (void)
  {
  	fprintf (stderr,
  			""
  			"  evacuation-threshold=P (where P is a percentage, an integer in 0-100)\n"
  			"  (no-)lazy-sweep\n"
  			"  (no-)concurrent-sweep\n"
  			);
  }
  
  /*
   * This callback is used to clear cards, move cards to the shadow table and do counting.
   */
  static void
  major_iterate_live_block_ranges (sgen_cardtable_block_callback callback)
  {
  	MSBlockInfo *block;
  	gboolean has_references;
  
  	major_finish_sweep_checking ();
  	FOREACH_BLOCK_HAS_REFERENCES_NO_LOCK (block, has_references) {
  		if (has_references)
  			callback ((mword)MS_BLOCK_FOR_BLOCK_INFO (block), MS_BLOCK_SIZE);
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  #ifdef HEAVY_STATISTICS
  extern guint64 marked_cards;
  extern guint64 scanned_cards;
  extern guint64 scanned_objects;
  extern guint64 remarked_cards;
  #endif
  
  #define CARD_WORDS_PER_BLOCK (CARDS_PER_BLOCK / SIZEOF_VOID_P)
  /*
   * MS blocks are 16K aligned.
   * Cardtables are 4K aligned, at least.
   * This means that the cardtable of a given block is 32 bytes aligned.
   */
  static guint8*
  initial_skip_card (guint8 *card_data)
  {
  	mword *cards = (mword*)card_data;
  	mword card;
  	int i;
  	for (i = 0; i < CARD_WORDS_PER_BLOCK; ++i) {
  		card = cards [i];
  		if (card)
  			break;
  	}
  
  	if (i == CARD_WORDS_PER_BLOCK)
  		return card_data + CARDS_PER_BLOCK;
  
  #if defined(__i386__) && defined(__GNUC__)
  	return card_data + i * 4 +  (__builtin_ffs (card) - 1) / 8;
  #elif defined(__x86_64__) && defined(__GNUC__)
  	return card_data + i * 8 +  (__builtin_ffsll (card) - 1) / 8;
  #elif defined(__s390x__) && defined(__GNUC__)
  	return card_data + i * 8 +  (__builtin_ffsll (GUINT64_TO_LE(card)) - 1) / 8;
  #else
  	for (i = i * SIZEOF_VOID_P; i < CARDS_PER_BLOCK; ++i) {
  		if (card_data [i])
  			return &card_data [i];
  	}
  	return card_data;
  #endif
  }
  
  #define MS_BLOCK_OBJ_INDEX_FAST(o,b,os)	(((char*)(o) - ((b) + MS_BLOCK_SKIP)) / (os))
  #define MS_BLOCK_OBJ_FAST(b,os,i)			((b) + MS_BLOCK_SKIP + (os) * (i))
  #define MS_OBJ_ALLOCED_FAST(o,b)		(*(void**)(o) && (*(char**)(o) < (b) || *(char**)(o) >= (b) + MS_BLOCK_SIZE))
  
  static void
  scan_card_table_for_block (MSBlockInfo *block, gboolean mod_union, ScanCopyContext ctx)
  {
  	SgenGrayQueue *queue = ctx.queue;
  	ScanObjectFunc scan_func = ctx.ops->scan_object;
  #ifndef SGEN_HAVE_OVERLAPPING_CARDS
  	guint8 cards_copy [CARDS_PER_BLOCK];
  #endif
  	gboolean small_objects;
  	int block_obj_size;
  	char *block_start;
  	guint8 *card_data, *card_base;
  	guint8 *card_data_end;
  	char *scan_front = NULL;
  
  	block_obj_size = block->obj_size;
  	small_objects = block_obj_size < CARD_SIZE_IN_BYTES;
  
  	block_start = MS_BLOCK_FOR_BLOCK_INFO (block);
  
  	/*
  	 * This is safe in face of card aliasing for the following reason:
  	 *
  	 * Major blocks are 16k aligned, or 32 cards aligned.
  	 * Cards aliasing happens in powers of two, so as long as major blocks are aligned to their
  	 * sizes, they won't overflow the cardtable overlap modulus.
  	 */
  	if (mod_union) {
  		card_data = card_base = block->cardtable_mod_union;
  		/*
  		 * This happens when the nursery collection that precedes finishing
  		 * the concurrent collection allocates new major blocks.
  		 */
  		if (!card_data)
  			return;
  	} else {
  #ifdef SGEN_HAVE_OVERLAPPING_CARDS
  		card_data = card_base = sgen_card_table_get_card_scan_address ((mword)block_start);
  #else
  		if (!sgen_card_table_get_card_data (cards_copy, (mword)block_start, CARDS_PER_BLOCK))
  			return;
  		card_data = card_base = cards_copy;
  #endif
  	}
  	card_data_end = card_data + CARDS_PER_BLOCK;
  
  	card_data += MS_BLOCK_SKIP >> CARD_BITS;
  
  	card_data = initial_skip_card (card_data);
  	while (card_data < card_data_end) {
  		size_t card_index, first_object_index;
  		char *start;
  		char *end;
  		char *first_obj, *obj;
  
  		HEAVY_STAT (++scanned_cards);
  
  		if (!*card_data) {
  			++card_data;
  			continue;
  		}
  
  		card_index = card_data - card_base;
  		start = (char*)(block_start + card_index * CARD_SIZE_IN_BYTES);
  		end = start + CARD_SIZE_IN_BYTES;
  
  		if (!block_is_swept_or_marking (block))
  			sweep_block (block);
  
  		HEAVY_STAT (++marked_cards);
  
  		if (small_objects)
  			sgen_card_table_prepare_card_for_scanning (card_data);
  
  		/*
  		 * If the card we're looking at starts at or in the block header, we
  		 * must start at the first object in the block, without calculating
  		 * the index of the object we're hypothetically starting at, because
  		 * it would be negative.
  		 */
  		if (card_index <= (MS_BLOCK_SKIP >> CARD_BITS))
  			first_object_index = 0;
  		else
  			first_object_index = MS_BLOCK_OBJ_INDEX_FAST (start, block_start, block_obj_size);
  
  		obj = first_obj = (char*)MS_BLOCK_OBJ_FAST (block_start, block_obj_size, first_object_index);
  
  		binary_protocol_card_scan (first_obj, end - first_obj);
  
  		while (obj < end) {
  			if (obj < scan_front || !MS_OBJ_ALLOCED_FAST (obj, block_start))
  				goto next_object;
  
  			if (mod_union) {
  				/* FIXME: do this more efficiently */
  				int w, b;
  				MS_CALC_MARK_BIT (w, b, obj);
  				if (!MS_MARK_BIT (block, w, b))
  					goto next_object;
  			}
  
  			GCObject *object = (GCObject*)obj;
  
  			if (small_objects) {
  				HEAVY_STAT (++scanned_objects);
  				scan_func (object, sgen_obj_get_descriptor (object), queue);
  			} else {
  				size_t offset = sgen_card_table_get_card_offset (obj, block_start);
  				sgen_cardtable_scan_object (object, block_obj_size, card_base + offset, mod_union, ctx);
  			}
  		next_object:
  			obj += block_obj_size;
  			g_assert (scan_front <= obj);
  			scan_front = obj;
  		}
  
  		HEAVY_STAT (if (*card_data) ++remarked_cards);
  
  		if (small_objects)
  			++card_data;
  		else
  			card_data = card_base + sgen_card_table_get_card_offset (obj, block_start);
  	}
  }
  
  static void
  major_scan_card_table (gboolean mod_union, ScanCopyContext ctx)
  {
  	MSBlockInfo *block;
  	gboolean has_references;
  
  	if (!concurrent_mark)
  		g_assert (!mod_union);
  
  	major_finish_sweep_checking ();
  	FOREACH_BLOCK_HAS_REFERENCES_NO_LOCK (block, has_references) {
  #ifdef PREFETCH_CARDS
  		int prefetch_index = __index + 6;
  		if (prefetch_index < allocated_blocks.next_slot) {
  			MSBlockInfo *prefetch_block = BLOCK_UNTAG (allocated_blocks.data [prefetch_index]);
  			guint8 *prefetch_cards = sgen_card_table_get_card_scan_address ((mword)MS_BLOCK_FOR_BLOCK_INFO (prefetch_block));
  			PREFETCH_READ (prefetch_block);
  			PREFETCH_WRITE (prefetch_cards);
  			PREFETCH_WRITE (prefetch_cards + 32);
                  }
  #endif
  
  		if (!has_references)
  			continue;
  
  		scan_card_table_for_block (block, mod_union, ctx);
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  static void
  major_count_cards (long long *num_total_cards, long long *num_marked_cards)
  {
  	MSBlockInfo *block;
  	gboolean has_references;
  	long long total_cards = 0;
  	long long marked_cards = 0;
  
  	if (sweep_in_progress ()) {
  		*num_total_cards = -1;
  		*num_marked_cards = -1;
  		return;
  	}
  
  	FOREACH_BLOCK_HAS_REFERENCES_NO_LOCK (block, has_references) {
  		guint8 *cards = sgen_card_table_get_card_scan_address ((mword) MS_BLOCK_FOR_BLOCK_INFO (block));
  		int i;
  
  		if (!has_references)
  			continue;
  
  		total_cards += CARDS_PER_BLOCK;
  		for (i = 0; i < CARDS_PER_BLOCK; ++i) {
  			if (cards [i])
  				++marked_cards;
  		}
  	} END_FOREACH_BLOCK_NO_LOCK;
  
  	*num_total_cards = total_cards;
  	*num_marked_cards = marked_cards;
  }
  
  static void
  update_cardtable_mod_union (void)
  {
  	MSBlockInfo *block;
  
  	FOREACH_BLOCK_NO_LOCK (block) {
  		size_t num_cards;
  		guint8 *mod_union = get_cardtable_mod_union_for_block (block, TRUE);
  		sgen_card_table_update_mod_union (mod_union, MS_BLOCK_FOR_BLOCK_INFO (block), MS_BLOCK_SIZE, &num_cards);
  		SGEN_ASSERT (6, num_cards == CARDS_PER_BLOCK, "Number of cards calculation is wrong");
  	} END_FOREACH_BLOCK_NO_LOCK;
  }
  
  #undef pthread_create
  
  static void
  post_param_init (SgenMajorCollector *collector)
  {
  	collector->sweeps_lazily = lazy_sweep;
  	collector->needs_thread_pool = concurrent_mark || concurrent_sweep;
  }
  
  static void
  sgen_marksweep_init_internal (SgenMajorCollector *collector, gboolean is_concurrent)
  {
  	int i;
  
  	sgen_register_fixed_internal_mem_type (INTERNAL_MEM_MS_BLOCK_INFO, sizeof (MSBlockInfo));
  
  	num_block_obj_sizes = ms_calculate_block_obj_sizes (MS_BLOCK_OBJ_SIZE_FACTOR, NULL);
  	block_obj_sizes = sgen_alloc_internal_dynamic (sizeof (int) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  	ms_calculate_block_obj_sizes (MS_BLOCK_OBJ_SIZE_FACTOR, block_obj_sizes);
  
  	evacuate_block_obj_sizes = sgen_alloc_internal_dynamic (sizeof (gboolean) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  	for (i = 0; i < num_block_obj_sizes; ++i)
  		evacuate_block_obj_sizes [i] = FALSE;
  
  	sweep_slots_available = sgen_alloc_internal_dynamic (sizeof (size_t) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  	sweep_slots_used = sgen_alloc_internal_dynamic (sizeof (size_t) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  	sweep_num_blocks = sgen_alloc_internal_dynamic (sizeof (size_t) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  
  	/*
  	{
  		int i;
  		g_print ("block object sizes:\n");
  		for (i = 0; i < num_block_obj_sizes; ++i)
  			g_print ("%d\n", block_obj_sizes [i]);
  	}
  	*/
  
  	for (i = 0; i < MS_BLOCK_TYPE_MAX; ++i)
  		free_block_lists [i] = sgen_alloc_internal_dynamic (sizeof (MSBlockInfo*) * num_block_obj_sizes, INTERNAL_MEM_MS_TABLES, TRUE);
  
  	for (i = 0; i < MS_NUM_FAST_BLOCK_OBJ_SIZE_INDEXES; ++i)
  		fast_block_obj_size_indexes [i] = ms_find_block_obj_size_index (i * 8);
  	for (i = 0; i < MS_NUM_FAST_BLOCK_OBJ_SIZE_INDEXES * 8; ++i)
  		g_assert (MS_BLOCK_OBJ_SIZE_INDEX (i) == ms_find_block_obj_size_index (i));
  
  	mono_counters_register ("# major blocks allocated", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_alloced);
  	mono_counters_register ("# major blocks freed", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_freed);
  	mono_counters_register ("# major blocks lazy swept", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_lazy_swept);
  	mono_counters_register ("# major objects evacuated", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_objects_evacuated);
  #if SIZEOF_VOID_P != 8
  	mono_counters_register ("# major blocks freed ideally", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_freed_ideal);
  	mono_counters_register ("# major blocks freed less ideally", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_freed_less_ideal);
  	mono_counters_register ("# major blocks freed individually", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_freed_individual);
  	mono_counters_register ("# major blocks allocated less ideally", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_major_blocks_alloced_less_ideal);
  #endif
  
  	collector->section_size = MAJOR_SECTION_SIZE;
  
  	concurrent_mark = is_concurrent;
  	collector->is_concurrent = is_concurrent;
  	collector->needs_thread_pool = is_concurrent || concurrent_sweep;
  	if (is_concurrent)
  		collector->want_synchronous_collection = &want_evacuation;
  	else
  		collector->want_synchronous_collection = NULL;
  	collector->get_and_reset_num_major_objects_marked = major_get_and_reset_num_major_objects_marked;
  	collector->supports_cardtable = TRUE;
  
  	collector->alloc_heap = major_alloc_heap;
  	collector->is_object_live = major_is_object_live;
  	collector->alloc_small_pinned_obj = major_alloc_small_pinned_obj;
  	collector->alloc_degraded = major_alloc_degraded;
  
  	collector->alloc_object = major_alloc_object;
  	collector->free_pinned_object = free_pinned_object;
  	collector->iterate_objects = major_iterate_objects;
  	collector->free_non_pinned_object = major_free_non_pinned_object;
  	collector->pin_objects = major_pin_objects;
  	collector->pin_major_object = pin_major_object;
  	collector->scan_card_table = major_scan_card_table;
  	collector->iterate_live_block_ranges = major_iterate_live_block_ranges;
  	if (is_concurrent) {
  		collector->update_cardtable_mod_union = update_cardtable_mod_union;
  		collector->get_cardtable_mod_union_for_reference = major_get_cardtable_mod_union_for_reference;
  	}
  	collector->init_to_space = major_init_to_space;
  	collector->sweep = major_sweep;
  	collector->have_swept = major_have_swept;
  	collector->finish_sweeping = major_finish_sweep_checking;
  	collector->free_swept_blocks = major_free_swept_blocks;
  	collector->check_scan_starts = major_check_scan_starts;
  	collector->dump_heap = major_dump_heap;
  	collector->get_used_size = major_get_used_size;
  	collector->start_nursery_collection = major_start_nursery_collection;
  	collector->finish_nursery_collection = major_finish_nursery_collection;
  	collector->start_major_collection = major_start_major_collection;
  	collector->finish_major_collection = major_finish_major_collection;
  	collector->ptr_is_in_non_pinned_space = major_ptr_is_in_non_pinned_space;
  	collector->ptr_is_from_pinned_alloc = ptr_is_from_pinned_alloc;
  	collector->report_pinned_memory_usage = major_report_pinned_memory_usage;
  	collector->get_num_major_sections = get_num_major_sections;
  	collector->get_bytes_survived_last_sweep = get_bytes_survived_last_sweep;
  	collector->handle_gc_param = major_handle_gc_param;
  	collector->print_gc_param_usage = major_print_gc_param_usage;
  	collector->post_param_init = post_param_init;
  	collector->is_valid_object = major_is_valid_object;
  	collector->describe_pointer = major_describe_pointer;
  	collector->count_cards = major_count_cards;
  
  	collector->major_ops_serial.copy_or_mark_object = major_copy_or_mark_object_canonical;
  	collector->major_ops_serial.scan_object = major_scan_object_with_evacuation;
  	collector->major_ops_serial.drain_gray_stack = drain_gray_stack;
  	if (is_concurrent) {
  		collector->major_ops_concurrent_start.copy_or_mark_object = major_copy_or_mark_object_concurrent_canonical;
  		collector->major_ops_concurrent_start.scan_object = major_scan_object_concurrent;
  		collector->major_ops_concurrent_start.drain_gray_stack = drain_gray_stack_concurrent;
  
  		collector->major_ops_concurrent_finish.copy_or_mark_object = major_copy_or_mark_object_concurrent_finish_canonical;
  		collector->major_ops_concurrent_finish.scan_object = major_scan_object_no_evacuation;
  		collector->major_ops_concurrent_finish.scan_vtype = major_scan_vtype_concurrent_finish;
  		collector->major_ops_concurrent_finish.drain_gray_stack = drain_gray_stack_no_evacuation;
  	}
  
  #ifdef HEAVY_STATISTICS
  	mono_counters_register ("Optimized copy", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy);
  	mono_counters_register ("Optimized copy nursery", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_nursery);
  	mono_counters_register ("Optimized copy nursery forwarded", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_nursery_forwarded);
  	mono_counters_register ("Optimized copy nursery pinned", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_nursery_pinned);
  	mono_counters_register ("Optimized copy major", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_major);
  	mono_counters_register ("Optimized copy major small fast", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_major_small_fast);
  	mono_counters_register ("Optimized copy major small slow", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_major_small_slow);
  	mono_counters_register ("Optimized copy major large", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_copy_major_large);
  	mono_counters_register ("Optimized major scan", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_major_scan);
  	mono_counters_register ("Optimized major scan no refs", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_optimized_major_scan_no_refs);
  
  	mono_counters_register ("Gray stack drain loops", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_drain_loops);
  	mono_counters_register ("Gray stack prefetch fills", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_drain_prefetch_fills);
  	mono_counters_register ("Gray stack prefetch failures", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_drain_prefetch_fill_failures);
  #endif
  
  #ifdef SGEN_HEAVY_BINARY_PROTOCOL
  	mono_os_mutex_init (&scanned_objects_list_lock);
  #endif
  
  	SGEN_ASSERT (0, SGEN_MAX_SMALL_OBJ_SIZE <= MS_BLOCK_FREE / 2, "MAX_SMALL_OBJ_SIZE must be at most MS_BLOCK_FREE / 2");
  
  	/*cardtable requires major pages to be 8 cards aligned*/
  	g_assert ((MS_BLOCK_SIZE % (8 * CARD_SIZE_IN_BYTES)) == 0);
  }
  
  void
  sgen_marksweep_init (SgenMajorCollector *collector)
  {
  	sgen_marksweep_init_internal (collector, FALSE);
  }
  
  void
  sgen_marksweep_conc_init (SgenMajorCollector *collector)
  {
  	sgen_marksweep_init_internal (collector, TRUE);
  }
  
  #endif
  