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Commit 17ce6ef8 authored by Liu Bo's avatar Liu Bo Committed by Chris Mason
Browse files

Btrfs: add a check to decide if we should defrag the range 



If our file's layout is as follows:
| hole | data1 | hole | data2 |

we do not need to defrag this file, because this file has holes and
cannot be merged into one extent.

Signed-off-by: default avatarLiu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 4cb13e5d

fs/btrfs/ioctl.c

+35 −1
Original line number Diff line number Diff line
@@ -784,6 +784,31 @@ 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)

{

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

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

	int ret = 0;



	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);

	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);



	return ret;

}



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

			       int thresh, u64 *last_len, u64 *skip,

			       u64 *defrag_end)
@@ -821,8 +846,16 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len, 
	}



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

	if (em->block_start >= EXTENT_MAP_LAST_BYTE)

	if (em->block_start >= EXTENT_MAP_LAST_BYTE) {

		ret = 0;

		goto out;

	}



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

	if (check_adjacent_extents(inode, em)) {

		ret = 0;

		goto out;

	}



	/*

	 * we hit a real extent, if it is big don't bother defragging it again
@@ -830,6 +863,7 @@ static int should_defrag_range(struct inode *inode, u64 start, u64 len, 
	if ((*last_len == 0 || *last_len >= thresh) && em->len >= thresh)

		ret = 0;



out:

	/*

	 * last_len ends up being a counter of how many bytes we've defragged.

	 * every time we choose not to defrag an extent, we reset *last_len