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Btrfs: Only let very young transactions grow during commit 

Commits are fairly expensive, and so btrfs has code to sit around for a while
during the commit and let new writers come in.

But, while we're sitting there, new delayed refs might be added, and those
can be expensive to process as well.  Unless the transaction is very very
young, it makes sense to go ahead and let the commit finish without hanging
around.

The commit grow loop isn't as important as it used to be, the fsync logging
code handles most performance critical syncs now.

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 66d7e85ea7
commit 89573b9c51
1 changed files with 10 additions and 3 deletions
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13
fs/btrfs/transaction.c
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@ -972,6 +972,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
struct extent_io_tree *pinned_copy;
DEFINE_WAIT(wait);
int ret;
int should_grow = 0;
unsigned long now = get_seconds();
/* make a pass through all the delayed refs we have so far
* any runnings procs may add more while we are here
@ -1029,6 +1031,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
}
}
if (now < cur_trans->start_time || now - cur_trans->start_time < 1)
should_grow = 1;
do {
int snap_pending = 0;
joined = cur_trans->num_joined;
@ -1041,7 +1046,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
if (cur_trans->num_writers > 1)
timeout = MAX_SCHEDULE_TIMEOUT;
else
else if (should_grow)
timeout = 1;
mutex_unlock(&root->fs_info->trans_mutex);
@ -1051,12 +1056,14 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
BUG_ON(ret);
}
schedule_timeout(timeout);
smp_mb();
if (cur_trans->num_writers > 1 || should_grow)
schedule_timeout(timeout);
mutex_lock(&root->fs_info->trans_mutex);
finish_wait(&cur_trans->writer_wait, &wait);
} while (cur_trans->num_writers > 1 ||
(cur_trans->num_joined != joined));
(should_grow && cur_trans->num_joined != joined));
ret = create_pending_snapshots(trans, root->fs_info);
BUG_ON(ret);