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Btrfs: reduce stalls during transaction commit

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To avoid deadlocks and reduce latencies during some critical operations, some
transaction writers are allowed to jump into the running transaction and make
it run a little longer, while others sit around and wait for the commit to
finish.

This is a bit unfair, especially when the callers that jump in do a bunch
of IO that makes all the others procs on the box wait.  This commit
reduces the stalls this produces by pre-reading file extent pointers
during btrfs_finish_ordered_io before the transaction is joined.

It also tunes the drop_snapshot code to politely wait for transactions
that have started writing out their delayed refs to finish.  This avoids
new delayed refs being flooded into the queue while we're trying to
close off the transaction.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
2009-03-12 20:12:45 -04:00
parent c3e69d58e8
commit b7ec40d784
4 changed files with 80 additions and 8 deletions
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3
fs/btrfs/extent-tree.c
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@@ -3797,7 +3797,8 @@ int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
break;
if (wret < 0)
ret = wret;
if (trans->transaction->in_commit) {
if (trans->transaction->in_commit ||
trans->transaction->delayed_refs.flushing) {
ret = -EAGAIN;
break;
}