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Btrfs: fix data allocation hint start 

Sometimes our start allocation hint when we cow a file can be either
EXTENT_HOLE or some other such place holder, which is not optimal.  So if we
find that our em->block_start is one of these special values, check to see
where the first block of the inode is stored, and use that as a hint.  If that
block is also a special value, just fallback on a hint of 0 and let the
allocator figure out a good place to put the data.

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Josef Bacik 2009-11-10 21:23:47 -05:00 committed by Chris Mason
parent 444528b3e6
commit 6346c93988
1 changed files with 16 additions and 2 deletions
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18
fs/btrfs/inode.c
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@ -743,8 +743,22 @@ static noinline int cow_file_range(struct inode *inode,
em = search_extent_mapping(&BTRFS_I(inode)->extent_tree,
start, num_bytes);
if (em) {
alloc_hint = em->block_start;
free_extent_map(em);
/*
* if block start isn't an actual block number then find the
* first block in this inode and use that as a hint. If that
* block is also bogus then just don't worry about it.
*/
if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
free_extent_map(em);
em = search_extent_mapping(em_tree, 0, 0);
if (em && em->block_start < EXTENT_MAP_LAST_BYTE)
alloc_hint = em->block_start;
if (em)
free_extent_map(em);
} else {
alloc_hint = em->block_start;
free_extent_map(em);
}
}
read_unlock(&BTRFS_I(inode)->extent_tree.lock);
btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);