linux-packaging-mono/mono/sgen/sgen-cardtable.c

/**
 * \file
 * Card table implementation for sgen
 *
 * Author:
 * 	Rodrigo Kumpera (rkumpera@novell.com)
 *
 * Copyright 2001-2003 Ximian, Inc
 * Copyright 2003-2010 Novell, Inc.
 * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
 * Copyright (C) 2012 Xamarin Inc
 *
 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
 */

#include "config.h"
#ifdef HAVE_SGEN_GC

#include <string.h>

#include "mono/sgen/sgen-gc.h"
#include "mono/sgen/sgen-cardtable.h"
#include "mono/sgen/sgen-memory-governor.h"
#include "mono/sgen/sgen-protocol.h"
#include "mono/sgen/sgen-layout-stats.h"
#include "mono/sgen/sgen-client.h"
#include "mono/sgen/gc-internal-agnostic.h"
#include "mono/utils/mono-memory-model.h"

//#define CARDTABLE_STATS

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif
#include <sys/types.h>

guint8 *sgen_cardtable;

static gboolean need_mod_union;

#ifdef HEAVY_STATISTICS
guint64 marked_cards;
guint64 scanned_cards;
guint64 scanned_objects;
guint64 remarked_cards;
static guint64 large_objects;
static guint64 bloby_objects;
#endif

mword
sgen_card_table_number_of_cards_in_range (mword address, mword size)
{
	mword end = address + MAX (1, size) - 1;
	return (end >> CARD_BITS) - (address >> CARD_BITS) + 1;
}

static void
sgen_card_table_wbarrier_set_field (GCObject *obj, gpointer field_ptr, GCObject* value)
{
	*(void**)field_ptr = value;
	if (need_mod_union || sgen_ptr_in_nursery (value))
		sgen_card_table_mark_address ((mword)field_ptr);
	sgen_dummy_use (value);
}

static void
sgen_card_table_wbarrier_arrayref_copy (gpointer dest_ptr, gpointer src_ptr, int count)
{
	gpointer *dest = (gpointer *)dest_ptr;
	gpointer *src = (gpointer *)src_ptr;

	/*overlapping that required backward copying*/
	if (src < dest && (src + count) > dest) {
		gpointer *start = dest;
		dest += count - 1;
		src += count - 1;

		for (; dest >= start; --src, --dest) {
			gpointer value = *src;
			SGEN_UPDATE_REFERENCE_ALLOW_NULL (dest, value);
			if (need_mod_union || sgen_ptr_in_nursery (value))
				sgen_card_table_mark_address ((mword)dest);
			sgen_dummy_use (value);
		}
	} else {
		gpointer *end = dest + count;
		for (; dest < end; ++src, ++dest) {
			gpointer value = *src;
			SGEN_UPDATE_REFERENCE_ALLOW_NULL (dest, value);
			if (need_mod_union || sgen_ptr_in_nursery (value))
				sgen_card_table_mark_address ((mword)dest);
			sgen_dummy_use (value);
		}
	}	
}

static void
sgen_card_table_wbarrier_value_copy (gpointer dest, gpointer src, int count, size_t element_size)
{
	size_t size = count * element_size;

	TLAB_ACCESS_INIT;
	ENTER_CRITICAL_REGION;

	mono_gc_memmove_atomic (dest, src, size);
	sgen_card_table_mark_range ((mword)dest, size);

	EXIT_CRITICAL_REGION;
}

static void
sgen_card_table_wbarrier_object_copy (GCObject* obj, GCObject *src)
{
	size_t size = sgen_client_par_object_get_size (SGEN_LOAD_VTABLE_UNCHECKED (obj), obj);

	TLAB_ACCESS_INIT;
	ENTER_CRITICAL_REGION;

	mono_gc_memmove_aligned ((char*)obj + SGEN_CLIENT_OBJECT_HEADER_SIZE, (char*)src + SGEN_CLIENT_OBJECT_HEADER_SIZE,
			size - SGEN_CLIENT_OBJECT_HEADER_SIZE);
	sgen_card_table_mark_range ((mword)obj, size);

	EXIT_CRITICAL_REGION;
}

static void
sgen_card_table_wbarrier_generic_nostore (gpointer ptr)
{
	sgen_card_table_mark_address ((mword)ptr);	
}

static void
sgen_card_table_wbarrier_range_copy (gpointer _dest, gpointer _src, int size)
{
	GCObject **dest = (GCObject **)_dest;
	GCObject **src = (GCObject **)_src;

	size_t nursery_bits = sgen_nursery_bits;
	char *start = sgen_nursery_start;
	G_GNUC_UNUSED char *end = sgen_nursery_end;

	/*
	 * It's cardtable theory time!
	 * Our cardtable scanning code supports marking any card that an object/valuetype belongs to.
	 * This function is supposed to be used to copy a range that fully belongs to a single type.
	 * It must not be used, for example, to copy 2 adjacent VTs in an array.
	*/
	volatile guint8 *card_address = (volatile guint8 *)sgen_card_table_get_card_address ((mword)dest);
	while (size) {
		GCObject *value = *src;
		*dest = value;
		if (SGEN_PTR_IN_NURSERY (value, nursery_bits, start, end) || sgen_concurrent_collection_in_progress) {
			*card_address = 1;
			sgen_dummy_use (value);
		}
		++src;
		++dest;
		size -= SIZEOF_VOID_P;
	}
}

#ifdef SGEN_HAVE_OVERLAPPING_CARDS

guint8 *sgen_shadow_cardtable;

#define SGEN_CARDTABLE_END (sgen_cardtable + CARD_COUNT_IN_BYTES)

static gboolean
sgen_card_table_region_begin_scanning (mword start, mword size)
{
	mword end = start + size;
	/*XXX this can be improved to work on words and have a single loop induction var */
	while (start < end) {
		if (sgen_card_table_card_begin_scanning (start))
			return TRUE;
		start += CARD_SIZE_IN_BYTES;
	}
	return FALSE;
}

#else

static gboolean
sgen_card_table_region_begin_scanning (mword start, mword size)
{
	gboolean res = FALSE;
	guint8 *card = sgen_card_table_get_card_address (start);
	guint8 *end = card + sgen_card_table_number_of_cards_in_range (start, size);

	/*XXX this can be improved to work on words and have a branchless body */
	while (card != end) {
		if (*card++) {
			res = TRUE;
			break;
		}
	}

	memset (sgen_card_table_get_card_address (start), 0, size >> CARD_BITS);

	return res;
}

#endif

/*FIXME this assumes that major blocks are multiple of 4K which is pretty reasonable */
gboolean
sgen_card_table_get_card_data (guint8 *data_dest, mword address, mword cards)
{
	mword *start = (mword*)sgen_card_table_get_card_scan_address (address);
	mword *dest = (mword*)data_dest;
	mword *end = (mword*)(data_dest + cards);
	mword mask = 0;

	for (; dest < end; ++dest, ++start) {
		mword v = *start;
		*dest = v;
		mask |= v;

#ifndef SGEN_HAVE_OVERLAPPING_CARDS
		*start = 0;
#endif
	}

	return mask != 0;
}

void*
sgen_card_table_align_pointer (void *ptr)
{
	return (void*)((mword)ptr & ~(CARD_SIZE_IN_BYTES - 1));
}

void
sgen_card_table_mark_range (mword address, mword size)
{
	mword num_cards = sgen_card_table_number_of_cards_in_range (address, size);
	guint8 *start = sgen_card_table_get_card_address (address);

#ifdef SGEN_HAVE_OVERLAPPING_CARDS
	/*
	 * FIXME: There's a theoretical bug here, namely that the card table is allocated so
	 * far toward the end of the address space that start + num_cards overflows.
	 */
	guint8 *end = start + num_cards;
	SGEN_ASSERT (0, num_cards <= CARD_COUNT_IN_BYTES, "How did we get an object larger than the card table?");
	if (end > SGEN_CARDTABLE_END) {
		memset (start, 1, SGEN_CARDTABLE_END - start);
		memset (sgen_cardtable, 1, end - SGEN_CARDTABLE_END);
		return;
	}
#endif

	memset (start, 1, num_cards);
}

static gboolean
sgen_card_table_is_range_marked (guint8 *cards, mword address, mword size)
{
	guint8 *end = cards + sgen_card_table_number_of_cards_in_range (address, size);

	/*This is safe since this function is only called by code that only passes continuous card blocks*/
	while (cards != end) {
		if (*cards++)
			return TRUE;
	}
	return FALSE;

}

static void
sgen_card_table_record_pointer (gpointer address)
{
	*sgen_card_table_get_card_address ((mword)address) = 1;
}

static gboolean
sgen_card_table_find_address (char *addr)
{
	return sgen_card_table_address_is_marked ((mword)addr);
}

static gboolean
sgen_card_table_find_address_with_cards (char *cards_start, guint8 *cards, char *addr)
{
	cards_start = (char *)sgen_card_table_align_pointer (cards_start);
	return cards [(addr - cards_start) >> CARD_BITS];
}

static void
update_mod_union (guint8 *dest, guint8 *start_card, size_t num_cards)
{
	int i;
	/* Marking from another thread can happen while we mark here */
	for (i = 0; i < num_cards; ++i) {
		if (start_card [i])
			dest [i] = 1;
	}
}

guint8*
sgen_card_table_alloc_mod_union (char *obj, mword obj_size)
{
	size_t num_cards = sgen_card_table_number_of_cards_in_range ((mword) obj, obj_size);
	guint8 *mod_union = (guint8 *)sgen_alloc_internal_dynamic (num_cards, INTERNAL_MEM_CARDTABLE_MOD_UNION, TRUE);
	memset (mod_union, 0, num_cards);
	return mod_union;
}

void
sgen_card_table_free_mod_union (guint8 *mod_union, char *obj, mword obj_size)
{
	size_t num_cards = sgen_card_table_number_of_cards_in_range ((mword) obj, obj_size);
	sgen_free_internal_dynamic (mod_union, num_cards, INTERNAL_MEM_CARDTABLE_MOD_UNION);
}

void
sgen_card_table_update_mod_union_from_cards (guint8 *dest, guint8 *start_card, size_t num_cards)
{
	SGEN_ASSERT (0, dest, "Why don't we have a mod union?");
	update_mod_union (dest, start_card, num_cards);
}

void
sgen_card_table_update_mod_union (guint8 *dest, char *obj, mword obj_size, size_t *out_num_cards)
{
	guint8 *start_card = sgen_card_table_get_card_address ((mword)obj);
#ifndef SGEN_HAVE_OVERLAPPING_CARDS
	guint8 *end_card = sgen_card_table_get_card_address ((mword)obj + obj_size - 1) + 1;
#endif
	size_t num_cards;

#ifdef SGEN_HAVE_OVERLAPPING_CARDS
	size_t rest;

	rest = num_cards = sgen_card_table_number_of_cards_in_range ((mword) obj, obj_size);

	while (start_card + rest > SGEN_CARDTABLE_END) {
		size_t count = SGEN_CARDTABLE_END - start_card;
		sgen_card_table_update_mod_union_from_cards (dest, start_card, count);
		dest += count;
		rest -= count;
		start_card = sgen_cardtable;
	}
	num_cards = rest;
#else
	num_cards = end_card - start_card;
#endif

	sgen_card_table_update_mod_union_from_cards (dest, start_card, num_cards);

	if (out_num_cards)
		*out_num_cards = num_cards;
}

/* Preclean cards and saves the cards that need to be scanned afterwards in cards_preclean */
void
sgen_card_table_preclean_mod_union (guint8 *cards, guint8 *cards_preclean, size_t num_cards)
{
	size_t i;

	memcpy (cards_preclean, cards, num_cards);
	for (i = 0; i < num_cards; i++) {
		if (cards_preclean [i]) {
			cards [i] = 0;
		}
	}
	/*
	 * When precleaning we need to make sure the card cleaning
	 * takes place before the object is scanned. If we don't
	 * do this we could finish scanning the object and, before
	 * the cleaning of the card takes place, another thread
	 * could dirty the object, mark the mod_union card only for
	 * us to clean it back, without scanning the object again.
	 */
	mono_memory_barrier ();
}

#ifdef SGEN_HAVE_OVERLAPPING_CARDS

static void
move_cards_to_shadow_table (mword start, mword size)
{
	guint8 *from = sgen_card_table_get_card_address (start);
	guint8 *to = sgen_card_table_get_shadow_card_address (start);
	size_t bytes = sgen_card_table_number_of_cards_in_range (start, size);

	if (bytes >= CARD_COUNT_IN_BYTES) {
		memcpy (sgen_shadow_cardtable, sgen_cardtable, CARD_COUNT_IN_BYTES);
	} else if (to + bytes > SGEN_SHADOW_CARDTABLE_END) {
		size_t first_chunk = SGEN_SHADOW_CARDTABLE_END - to;
		size_t second_chunk = MIN (CARD_COUNT_IN_BYTES, bytes) - first_chunk;

		memcpy (to, from, first_chunk);
		memcpy (sgen_shadow_cardtable, sgen_cardtable, second_chunk);
	} else {
		memcpy (to, from, bytes);
	}
}

static void
clear_cards (mword start, mword size)
{
	guint8 *addr = sgen_card_table_get_card_address (start);
	size_t bytes = sgen_card_table_number_of_cards_in_range (start, size);

	if (bytes >= CARD_COUNT_IN_BYTES) {
		memset (sgen_cardtable, 0, CARD_COUNT_IN_BYTES);
	} else if (addr + bytes > SGEN_CARDTABLE_END) {
		size_t first_chunk = SGEN_CARDTABLE_END - addr;

		memset (addr, 0, first_chunk);
		memset (sgen_cardtable, 0, bytes - first_chunk);
	} else {
		memset (addr, 0, bytes);
	}
}


#else

static void
clear_cards (mword start, mword size)
{
	memset (sgen_card_table_get_card_address (start), 0, sgen_card_table_number_of_cards_in_range (start, size));
}


#endif

static void
sgen_card_table_clear_cards (void)
{
	/*XXX we could do this in 2 ways. using mincore or iterating over all sections/los objects */
	sgen_major_collector_iterate_block_ranges (clear_cards);
	sgen_los_iterate_live_block_ranges (clear_cards);
	sgen_wbroots_iterate_live_block_ranges (clear_cards);
}

static void
sgen_card_table_start_scan_remsets (void)
{
#ifdef SGEN_HAVE_OVERLAPPING_CARDS
	/*FIXME we should have a bit on each block/los object telling if the object have marked cards.*/
	/*First we copy*/
	sgen_major_collector_iterate_block_ranges (move_cards_to_shadow_table);
	sgen_los_iterate_live_block_ranges (move_cards_to_shadow_table);
	sgen_wbroots_iterate_live_block_ranges (move_cards_to_shadow_table);

	/*Then we clear*/
	sgen_card_table_clear_cards ();
#endif
}

guint8*
sgen_get_card_table_configuration (int *shift_bits, gpointer *mask)
{
#ifndef MANAGED_WBARRIER
	return NULL;
#else
	if (!sgen_cardtable)
		return NULL;

	*shift_bits = CARD_BITS;
#ifdef SGEN_HAVE_OVERLAPPING_CARDS
	*mask = (gpointer)CARD_MASK;
#else
	*mask = NULL;
#endif

	return sgen_cardtable;
#endif
}

#if 0
void
sgen_card_table_dump_obj_card (GCObject *object, size_t size, void *dummy)
{
	guint8 *start = sgen_card_table_get_card_scan_address (object);
	guint8 *end = start + sgen_card_table_number_of_cards_in_range (object, size);
	int cnt = 0;
	printf ("--obj %p %d cards [%p %p]--", object, size, start, end);
	for (; start < end; ++start) {
		if (cnt == 0)
			printf ("\n\t[%p] ", start);
		printf ("%x ", *start);
		++cnt;
		if (cnt == 8)
			cnt = 0;
	}
	printf ("\n");
}
#endif

/*
 * Cardtable scanning
 */

#define MWORD_MASK (sizeof (mword) - 1)

static inline int
find_card_offset (mword card)
{
/*XXX Use assembly as this generates some pretty bad code */
#if (defined(__i386__) || defined(__arm__)) && defined(__GNUC__)
	return  (__builtin_ffs (card) - 1) / 8;
#elif (defined(__x86_64__) || defined(__aarch64__)) && defined(__GNUC__)
	return (__builtin_ffsll (card) - 1) / 8;
#elif defined(__s390x__)
	return (__builtin_ffsll (GUINT64_TO_LE(card)) - 1) / 8;
#else
	int i;
	guint8 *ptr = (guint8 *) &card;
	for (i = 0; i < sizeof (mword); ++i) {
		if (ptr[i])
			return i;
	}
	return 0;
#endif
}

guint8*
sgen_find_next_card (guint8 *card_data, guint8 *end)
{
	mword *cards, *cards_end;
	mword card;

	while ((((mword)card_data) & MWORD_MASK) && card_data < end) {
		if (*card_data)
			return card_data;
		++card_data;
	}

	if (card_data == end)
		return end;

	cards = (mword*)card_data;
	cards_end = (mword*)((mword)end & ~MWORD_MASK);
	while (cards < cards_end) {
		card = *cards;
		if (card)
			return (guint8*)cards + find_card_offset (card);
		++cards;
	}

	card_data = (guint8*)cards_end;
	while (card_data < end) {
		if (*card_data)
			return card_data;
		++card_data;
	}

	return end;
}

void
sgen_cardtable_scan_object (GCObject *obj, mword block_obj_size, guint8 *cards, ScanCopyContext ctx)
{
	HEAVY_STAT (++large_objects);

	if (sgen_client_cardtable_scan_object (obj, cards, ctx))
		return;

	HEAVY_STAT (++bloby_objects);
	if (cards) {
		if (sgen_card_table_is_range_marked (cards, (mword)obj, block_obj_size))
			ctx.ops->scan_object (obj, sgen_obj_get_descriptor (obj), ctx.queue);
	} else if (sgen_card_table_region_begin_scanning ((mword)obj, block_obj_size)) {
		ctx.ops->scan_object (obj, sgen_obj_get_descriptor (obj), ctx.queue);
	}

	sgen_binary_protocol_card_scan (obj, sgen_safe_object_get_size (obj));
}

void
sgen_card_table_init (SgenRememberedSet *remset)
{
	sgen_cardtable = (guint8 *)sgen_alloc_os_memory (CARD_COUNT_IN_BYTES, (SgenAllocFlags)(SGEN_ALLOC_INTERNAL | SGEN_ALLOC_ACTIVATE), "card table", MONO_MEM_ACCOUNT_SGEN_CARD_TABLE);

#ifdef SGEN_HAVE_OVERLAPPING_CARDS
	sgen_shadow_cardtable = (guint8 *)sgen_alloc_os_memory (CARD_COUNT_IN_BYTES, (SgenAllocFlags)(SGEN_ALLOC_INTERNAL | SGEN_ALLOC_ACTIVATE), "shadow card table", MONO_MEM_ACCOUNT_SGEN_SHADOW_CARD_TABLE);
#endif

#ifdef HEAVY_STATISTICS
	mono_counters_register ("marked cards", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &marked_cards);
	mono_counters_register ("scanned cards", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &scanned_cards);
	mono_counters_register ("remarked cards", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &remarked_cards);

	mono_counters_register ("cardtable scanned objects", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &scanned_objects);
	mono_counters_register ("cardtable large objects", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &large_objects);
	mono_counters_register ("cardtable bloby objects", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &bloby_objects);
#endif

	remset->wbarrier_set_field = sgen_card_table_wbarrier_set_field;
	remset->wbarrier_arrayref_copy = sgen_card_table_wbarrier_arrayref_copy;
	remset->wbarrier_value_copy = sgen_card_table_wbarrier_value_copy;
	remset->wbarrier_object_copy = sgen_card_table_wbarrier_object_copy;
	remset->wbarrier_generic_nostore = sgen_card_table_wbarrier_generic_nostore;
	remset->record_pointer = sgen_card_table_record_pointer;

	remset->start_scan_remsets = sgen_card_table_start_scan_remsets;

	remset->clear_cards = sgen_card_table_clear_cards;

	remset->find_address = sgen_card_table_find_address;
	remset->find_address_with_cards = sgen_card_table_find_address_with_cards;
	remset->wbarrier_range_copy = sgen_card_table_wbarrier_range_copy;

	need_mod_union = sgen_get_major_collector ()->is_concurrent;
}

#endif /*HAVE_SGEN_GC*/