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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: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Liu Bo 2012-03-29 09:57:45 -04:00 committed by Chris Mason
parent 4cb13e5d6e
commit 17ce6ef8d7
1 changed files with 35 additions and 1 deletions
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36
fs/btrfs/ioctl.c
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@ -784,6 +784,31 @@ none:
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