Commit 13c5a93e authored by Josef Bacik's avatar Josef Bacik
Browse files

Btrfs: avoid taking the trans_mutex in btrfs_end_transaction 



I've been working on making our O_DIRECT latency not suck and I noticed we were
taking the trans_mutex in btrfs_end_transaction.  So to do this we convert
num_writers and use_count to atomic_t's and just decrement them in
btrfs_end_transaction.  Instead of deleting the transaction from the trans list
in put_transaction we do that in btrfs_commit_transaction() since that's the
only time it actually needs to be removed from the list.  Thanks,

Signed-off-by: default avatarJosef Bacik <josef@redhat.com>
parent 93a54bc4

fs/btrfs/disk-io.c

+1 −1
Original line number Diff line number Diff line
@@ -3136,7 +3136,7 @@ static int btrfs_cleanup_transaction(struct btrfs_root *root) 
		btrfs_destroy_pinned_extent(root,

					    root->fs_info->pinned_extents);



		t->use_count = 0;

		atomic_set(&t->use_count, 0);

		list_del_init(&t->list);

		memset(t, 0, sizeof(*t));

		kmem_cache_free(btrfs_transaction_cachep, t);

fs/btrfs/transaction.c

+16 −21
Original line number Diff line number Diff line
@@ -32,10 +32,8 @@ 


static noinline void put_transaction(struct btrfs_transaction *transaction)

{

	WARN_ON(transaction->use_count == 0);

	transaction->use_count--;

	if (transaction->use_count == 0) {

		list_del_init(&transaction->list);

	WARN_ON(atomic_read(&transaction->use_count) == 0);

	if (atomic_dec_and_test(&transaction->use_count)) {

		memset(transaction, 0, sizeof(*transaction));

		kmem_cache_free(btrfs_transaction_cachep, transaction);

	}
@@ -60,14 +58,14 @@ static noinline int join_transaction(struct btrfs_root *root) 
		if (!cur_trans)

			return -ENOMEM;

		root->fs_info->generation++;

		cur_trans->num_writers = 1;

		atomic_set(&cur_trans->num_writers, 1);

		cur_trans->num_joined = 0;

		cur_trans->transid = root->fs_info->generation;

		init_waitqueue_head(&cur_trans->writer_wait);

		init_waitqueue_head(&cur_trans->commit_wait);

		cur_trans->in_commit = 0;

		cur_trans->blocked = 0;

		cur_trans->use_count = 1;

		atomic_set(&cur_trans->use_count, 1);

		cur_trans->commit_done = 0;

		cur_trans->start_time = get_seconds();
@@ -88,7 +86,7 @@ static noinline int join_transaction(struct btrfs_root *root) 
		root->fs_info->running_transaction = cur_trans;

		spin_unlock(&root->fs_info->new_trans_lock);

	} else {

		cur_trans->num_writers++;

		atomic_inc(&cur_trans->num_writers);

		cur_trans->num_joined++;

	}
@@ -145,7 +143,7 @@ static void wait_current_trans(struct btrfs_root *root) 
	cur_trans = root->fs_info->running_transaction;

	if (cur_trans && cur_trans->blocked) {

		DEFINE_WAIT(wait);

		cur_trans->use_count++;

		atomic_inc(&cur_trans->use_count);

		while (1) {

			prepare_to_wait(&root->fs_info->transaction_wait, &wait,

					TASK_UNINTERRUPTIBLE);
@@ -205,7 +203,7 @@ again: 
	}



	cur_trans = root->fs_info->running_transaction;

	cur_trans->use_count++;

	atomic_inc(&cur_trans->use_count);

	if (type != TRANS_JOIN_NOLOCK)

		mutex_unlock(&root->fs_info->trans_mutex);
@@ -336,7 +334,7 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid) 
			goto out_unlock;  /* nothing committing|committed */

	}



	cur_trans->use_count++;

	atomic_inc(&cur_trans->use_count);

	mutex_unlock(&root->fs_info->trans_mutex);



	wait_for_commit(root, cur_trans);
@@ -466,18 +464,14 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, 
			wake_up_process(info->transaction_kthread);

	}



	if (lock)

		mutex_lock(&info->trans_mutex);

	WARN_ON(cur_trans != info->running_transaction);

	WARN_ON(cur_trans->num_writers < 1);

	cur_trans->num_writers--;

	WARN_ON(atomic_read(&cur_trans->num_writers) < 1);

	atomic_dec(&cur_trans->num_writers);



	smp_mb();

	if (waitqueue_active(&cur_trans->writer_wait))

		wake_up(&cur_trans->writer_wait);

	put_transaction(cur_trans);

	if (lock)

		mutex_unlock(&info->trans_mutex);



	if (current->journal_info == trans)

		current->journal_info = NULL;
@@ -1187,7 +1181,7 @@ int btrfs_commit_transaction_async(struct btrfs_trans_handle *trans, 
	/* take transaction reference */

	mutex_lock(&root->fs_info->trans_mutex);

	cur_trans = trans->transaction;

	cur_trans->use_count++;

	atomic_inc(&cur_trans->use_count);

	mutex_unlock(&root->fs_info->trans_mutex);



	btrfs_end_transaction(trans, root);
@@ -1246,7 +1240,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, 


	mutex_lock(&root->fs_info->trans_mutex);

	if (cur_trans->in_commit) {

		cur_trans->use_count++;

		atomic_inc(&cur_trans->use_count);

		mutex_unlock(&root->fs_info->trans_mutex);

		btrfs_end_transaction(trans, root);
@@ -1268,7 +1262,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, 
		prev_trans = list_entry(cur_trans->list.prev,

					struct btrfs_transaction, list);

		if (!prev_trans->commit_done) {

			prev_trans->use_count++;

			atomic_inc(&prev_trans->use_count);

			mutex_unlock(&root->fs_info->trans_mutex);



			wait_for_commit(root, prev_trans);
@@ -1309,14 +1303,14 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, 
				TASK_UNINTERRUPTIBLE);



		smp_mb();

		if (cur_trans->num_writers > 1)

		if (atomic_read(&cur_trans->num_writers) > 1)

			schedule_timeout(MAX_SCHEDULE_TIMEOUT);

		else if (should_grow)

			schedule_timeout(1);



		mutex_lock(&root->fs_info->trans_mutex);

		finish_wait(&cur_trans->writer_wait, &wait);

	} while (cur_trans->num_writers > 1 ||

	} while (atomic_read(&cur_trans->num_writers) > 1 ||

		 (should_grow && cur_trans->num_joined != joined));



	ret = create_pending_snapshots(trans, root->fs_info);
@@ -1403,6 +1397,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, 


	wake_up(&cur_trans->commit_wait);



	list_del_init(&cur_trans->list);

	put_transaction(cur_trans);

	put_transaction(cur_trans);

fs/btrfs/transaction.h

+2 −2
Original line number Diff line number Diff line
@@ -27,11 +27,11 @@ struct btrfs_transaction { 
	 * total writers in this transaction, it must be zero before the

	 * transaction can end

	 */

	unsigned long num_writers;

	atomic_t num_writers;



	unsigned long num_joined;

	int in_commit;

	int use_count;

	atomic_t use_count;

	int commit_done;

	int blocked;

	struct list_head list;

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