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Commit 6c282eb4 authored by Li Zefan's avatar Li Zefan Committed by Chris Mason
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Btrfs: fix defrag regression 



If a file has 3 small extents:

| ext1 | ext2 | ext3 |

Running "btrfs fi defrag" will only defrag the last two extents, if those
extent mappings hasn't been read into memory from disk.

This bug was introduced by commit 17ce6ef8
("Btrfs: add a check to decide if we should defrag the range")

The cause is, that commit looked into previous and next extents using
lookup_extent_mapping() only.

While at it, remove the code that checks the previous extent, since
it's sufficient to check the next extent.

Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
parent 7ddf5a42

fs/btrfs/ioctl.c

+49 −48
Original line number Diff line number Diff line
@@ -786,39 +786,57 @@ static int find_new_extents(struct btrfs_root *root, 
	return -ENOENT;

}



/*

 * Validaty check of prev em and next em:

 * 1) no prev/next em

 * 2) prev/next em is an hole/inline extent

 */

static int check_adjacent_extents(struct inode *inode, struct extent_map *em)

static struct extent_map *defrag_lookup_extent(struct inode *inode, u64 start)

{

	struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;

	struct extent_map *prev = NULL, *next = NULL;

	int ret = 0;

	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;

	struct extent_map *em;

	u64 len = PAGE_CACHE_SIZE;



	/*

	 * hopefully we have this extent in the tree already, try without

	 * the full extent lock

	 */

	read_lock(&em_tree->lock);

	prev = lookup_extent_mapping(em_tree, em->start - 1, (u64)-1);

	next = lookup_extent_mapping(em_tree, em->start + em->len, (u64)-1);

	em = lookup_extent_mapping(em_tree, start, len);

	read_unlock(&em_tree->lock);



	if ((!prev || prev->block_start >= EXTENT_MAP_LAST_BYTE) &&

	    (!next || next->block_start >= EXTENT_MAP_LAST_BYTE))

		ret = 1;

	free_extent_map(prev);

	free_extent_map(next);

	if (!em) {

		/* get the big lock and read metadata off disk */

		lock_extent(io_tree, start, start + len - 1);

		em = btrfs_get_extent(inode, NULL, 0, start, len, 0);

		unlock_extent(io_tree, start, start + len - 1);



		if (IS_ERR(em))

			return NULL;

	}



	return em;

}



static bool defrag_check_next_extent(struct inode *inode, struct extent_map *em)

{

	struct extent_map *next;

	bool ret = true;



	/* this is the last extent */

	if (em->start + em->len >= i_size_read(inode))

		return false;



	next = defrag_lookup_extent(inode, em->start + em->len);

	if (!next || next->block_start >= EXTENT_MAP_LAST_BYTE)

		ret = false;



	free_extent_map(next);

	return ret;

}



static int should_defrag_range(struct inode *inode, u64 start, u64 len,

			       int thresh, u64 *last_len, u64 *skip,

			       u64 *defrag_end)

static int should_defrag_range(struct inode *inode, u64 start, int thresh,

			       u64 *last_len, u64 *skip, u64 *defrag_end)

{

	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;

	struct extent_map *em = NULL;

	struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;

	struct extent_map *em;

	int ret = 1;

	bool next_mergeable = true;



	/*

	 * make sure that once we start defragging an extent, we keep on
@@ -829,23 +847,9 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len, 


	*skip = 0;



	/*

	 * hopefully we have this extent in the tree already, try without

	 * the full extent lock

	 */

	read_lock(&em_tree->lock);

	em = lookup_extent_mapping(em_tree, start, len);

	read_unlock(&em_tree->lock);



	if (!em) {

		/* get the big lock and read metadata off disk */

		lock_extent(io_tree, start, start + len - 1);

		em = btrfs_get_extent(inode, NULL, 0, start, len, 0);

		unlock_extent(io_tree, start, start + len - 1);



		if (IS_ERR(em))

	em = defrag_lookup_extent(inode, start);

	if (!em)

		return 0;

	}



	/* this will cover holes, and inline extents */

	if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
@@ -853,18 +857,15 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len, 
		goto out;

	}



	/* If we have nothing to merge with us, just skip. */

	if (check_adjacent_extents(inode, em)) {

		ret = 0;

		goto out;

	}

	next_mergeable = defrag_check_next_extent(inode, em);



	/*

	 * we hit a real extent, if it is big don't bother defragging it again

	 * we hit a real extent, if it is big or the next extent is not a

	 * real extent, don't bother defragging it

	 */

	if ((*last_len == 0 || *last_len >= thresh) && em->len >= thresh)

	if ((*last_len == 0 || *last_len >= thresh) &&

	    (em->len >= thresh || !next_mergeable))

		ret = 0;



out:

	/*

	 * last_len ends up being a counter of how many bytes we've defragged.
@@ -1143,8 +1144,8 @@ int btrfs_defrag_file(struct inode *inode, struct file *file, 
			break;



		if (!should_defrag_range(inode, (u64)i << PAGE_CACHE_SHIFT,

					 PAGE_CACHE_SIZE, extent_thresh,

					 &last_len, &skip, &defrag_end)) {

					 extent_thresh, &last_len, &skip,

					 &defrag_end)) {

			unsigned long next;

			/*

			 * the should_defrag function tells us how much to skip