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Commit eabe0444 authored by Andrey Sidorov's avatar Andrey Sidorov Committed by Theodore Ts'o
Browse files

ext4: speed-up releasing blocks on commit 



Improve mb_free_blocks speed by clearing entire range at once instead
of iterating over each bit. Freeing block-by-block also makes buddy
bitmap subtree flip twice making most of the work a no-op. Very few
bits in buddy bitmap require change, e.g. freeing entire group is a 1
bit flip only.  As a result, releasing blocks of 60G file now takes
5ms instead of 2.7s.  This is especially good for non-preemptive
kernels as there is no rescheduling during release.

Signed-off-by: default avatarAndrey Sidorov <qrxd43@motorola.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 5c1ff336

fs/ext4/mballoc.c

+172 −61
Original line number Diff line number Diff line
@@ -405,6 +405,12 @@ static inline void mb_clear_bit(int bit, void *addr) 
	ext4_clear_bit(bit, addr);

}



static inline int mb_test_and_clear_bit(int bit, void *addr)

{

	addr = mb_correct_addr_and_bit(&bit, addr);

	return ext4_test_and_clear_bit(bit, addr);

}



static inline int mb_find_next_zero_bit(void *addr, int max, int start)

{

	int fix = 0, ret, tmpmax;
@@ -764,6 +770,24 @@ void ext4_mb_generate_buddy(struct super_block *sb, 
	spin_unlock(&EXT4_SB(sb)->s_bal_lock);

}



static void mb_regenerate_buddy(struct ext4_buddy *e4b)

{

	int count;

	int order = 1;

	void *buddy;



	while ((buddy = mb_find_buddy(e4b, order++, &count))) {

		ext4_set_bits(buddy, 0, count);

	}

	e4b->bd_info->bb_fragments = 0;

	memset(e4b->bd_info->bb_counters, 0,

		sizeof(*e4b->bd_info->bb_counters) *

		(e4b->bd_sb->s_blocksize_bits + 2));



	ext4_mb_generate_buddy(e4b->bd_sb, e4b->bd_buddy,

		e4b->bd_bitmap, e4b->bd_group);

}



/* The buddy information is attached the buddy cache inode

 * for convenience. The information regarding each group

 * is loaded via ext4_mb_load_buddy. The information involve
@@ -1246,6 +1270,33 @@ static void mb_clear_bits(void *bm, int cur, int len) 
	}

}



/* clear bits in given range

 * will return first found zero bit if any, -1 otherwise

 */

static int mb_test_and_clear_bits(void *bm, int cur, int len)

{

	__u32 *addr;

	int zero_bit = -1;



	len = cur + len;

	while (cur < len) {

		if ((cur & 31) == 0 && (len - cur) >= 32) {

			/* fast path: clear whole word at once */

			addr = bm + (cur >> 3);

			if (*addr != (__u32)(-1) && zero_bit == -1)

				zero_bit = cur + mb_find_next_zero_bit(addr, 32, 0);

			*addr = 0;

			cur += 32;

			continue;

		}

		if (!mb_test_and_clear_bit(cur, bm) && zero_bit == -1)

			zero_bit = cur;

		cur++;

	}



	return zero_bit;

}



void ext4_set_bits(void *bm, int cur, int len)

{

	__u32 *addr;
@@ -1264,17 +1315,90 @@ void ext4_set_bits(void *bm, int cur, int len) 
	}

}



/*

 * _________________________________________________________________ */



static inline int mb_buddy_adjust_border(int* bit, void* bitmap, int side)

{

	if (mb_test_bit(*bit + side, bitmap)) {

		mb_clear_bit(*bit, bitmap);

		(*bit) -= side;

		return 1;

	}

	else {

		(*bit) += side;

		mb_set_bit(*bit, bitmap);

		return -1;

	}

}



static void mb_buddy_mark_free(struct ext4_buddy *e4b, int first, int last)

{

	int max;

	int order = 1;

	void *buddy = mb_find_buddy(e4b, order, &max);



	while (buddy) {

		void *buddy2;



		/* Bits in range [first; last] are known to be set since

		 * corresponding blocks were allocated. Bits in range

		 * (first; last) will stay set because they form buddies on

		 * upper layer. We just deal with borders if they don't

		 * align with upper layer and then go up.

		 * Releasing entire group is all about clearing

		 * single bit of highest order buddy.

		 */



		/* Example:

		 * ---------------------------------

		 * |   1   |   1   |   1   |   1   |

		 * ---------------------------------

		 * | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |

		 * ---------------------------------

		 *   0   1   2   3   4   5   6   7

		 *      \_____________________/

		 *

		 * Neither [1] nor [6] is aligned to above layer.

		 * Left neighbour [0] is free, so mark it busy,

		 * decrease bb_counters and extend range to

		 * [0; 6]

		 * Right neighbour [7] is busy. It can't be coaleasced with [6], so

		 * mark [6] free, increase bb_counters and shrink range to

		 * [0; 5].

		 * Then shift range to [0; 2], go up and do the same.

		 */





		if (first & 1)

			e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&first, buddy, -1);

		if (!(last & 1))

			e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&last, buddy, 1);

		if (first > last)

			break;

		order++;



		if (first == last || !(buddy2 = mb_find_buddy(e4b, order, &max))) {

			mb_clear_bits(buddy, first, last - first + 1);

			e4b->bd_info->bb_counters[order - 1] += last - first + 1;

			break;

		}

		first >>= 1;

		last >>= 1;

		buddy = buddy2;

	}

}



static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,

			   int first, int count)

{

	int block = 0;

	int max = 0;

	int order;

	void *buddy;

	void *buddy2;

	int left_is_free = 0;

	int right_is_free = 0;

	int block;

	int last = first + count - 1;

	struct super_block *sb = e4b->bd_sb;



	BUG_ON(first + count > (sb->s_blocksize << 3));

	BUG_ON(last >= (sb->s_blocksize << 3));

	assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));

	mb_check_buddy(e4b);

	mb_free_blocks_double(inode, e4b, first, count);
@@ -1283,22 +1407,16 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, 
	if (first < e4b->bd_info->bb_first_free)

		e4b->bd_info->bb_first_free = first;



	/* let's maintain fragments counter */

	/* access memory sequentially: check left neighbour,

	 * clear range and then check right neighbour

	 */

	if (first != 0)

		block = !mb_test_bit(first - 1, e4b->bd_bitmap);

	if (first + count < EXT4_SB(sb)->s_mb_maxs[0])

		max = !mb_test_bit(first + count, e4b->bd_bitmap);

	if (block && max)

		e4b->bd_info->bb_fragments--;

	else if (!block && !max)

		e4b->bd_info->bb_fragments++;

		left_is_free = !mb_test_bit(first - 1, e4b->bd_bitmap);

	block = mb_test_and_clear_bits(e4b->bd_bitmap, first, count);

	if (last + 1 < EXT4_SB(sb)->s_mb_maxs[0])

		right_is_free = !mb_test_bit(last + 1, e4b->bd_bitmap);



	/* let's maintain buddy itself */

	while (count-- > 0) {

		block = first++;

		order = 0;



		if (!mb_test_bit(block, e4b->bd_bitmap)) {

	if (unlikely(block != -1)) {

		ext4_fsblk_t blocknr;



		blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
@@ -1308,42 +1426,35 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, 
				      blocknr,

				      "freeing already freed block "

				      "(bit %u)", block);

		mb_regenerate_buddy(e4b);

		goto done;

	}

		mb_clear_bit(block, e4b->bd_bitmap);

		e4b->bd_info->bb_counters[order]++;



		/* start of the buddy */

		buddy = mb_find_buddy(e4b, order, &max);



		do {

			block &= ~1UL;

			if (mb_test_bit(block, buddy) ||

					mb_test_bit(block + 1, buddy))

				break;



			/* both the buddies are free, try to coalesce them */

			buddy2 = mb_find_buddy(e4b, order + 1, &max);



			if (!buddy2)

				break;

	/* let's maintain fragments counter */

	if (left_is_free && right_is_free)

		e4b->bd_info->bb_fragments--;

	else if (!left_is_free && !right_is_free)

		e4b->bd_info->bb_fragments++;



			if (order > 0) {

				/* for special purposes, we don't set

				 * free bits in bitmap */

				mb_set_bit(block, buddy);

				mb_set_bit(block + 1, buddy);

	/* buddy[0] == bd_bitmap is a special case, so handle

	 * it right away and let mb_buddy_mark_free stay free of

	 * zero order checks.

	 * Check if neighbours are to be coaleasced,

	 * adjust bitmap bb_counters and borders appropriately.

	 */

	if (first & 1) {

		first += !left_is_free;

		e4b->bd_info->bb_counters[0] += left_is_free ? -1 : 1;

	}

	if (!(last & 1)) {

		last -= !right_is_free;

		e4b->bd_info->bb_counters[0] += right_is_free ? -1 : 1;

	}

			e4b->bd_info->bb_counters[order]--;

			e4b->bd_info->bb_counters[order]--;



			block = block >> 1;

			order++;

			e4b->bd_info->bb_counters[order]++;

	if (first <= last)

		mb_buddy_mark_free(e4b, first >> 1, last >> 1);



			mb_clear_bit(block, buddy2);

			buddy = buddy2;

		} while (1);

	}

done:

	mb_set_largest_free_order(sb, e4b->bd_info);

	mb_check_buddy(e4b);

}