Commit df57dbe6 authored Jul 23, 2012 by Liu Bo Committed by Chris Mason Jul 23, 2012

Btrfs: make btrfs's allocation smoothly with preallocation



For backref walking, we've introduce delayed ref's sequence.  However,
it changes our preallocation behavior.

The story is that when we preallocate an extent and then mark it written
piece by piece, the ideal case should be that we don't need to COW the
extent, which is why we use 'preallocate'.

But we may not make use of preallocation, since when we check for cross refs on
the extent, we may have two ref entries which have the same content except
the sequence value, and we recognize them as cross refs and do COW to allocate
another extent.

So we end up with several pieces of space instead of an whole extent.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

parent 51561ffe

fs/btrfs/extent-tree.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -2581,8 +2581,10 @@ static noinline int check_delayed_ref(struct btrfs_trans_handle *trans,

		node = rb_prev(node);
		if (node) {
		int seq = ref->seq;

		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
		if (ref->bytenr == bytenr)
		if (ref->bytenr == bytenr && ref->seq == seq)
		goto out_unlock;
		}

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