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Commit ff782e0a authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
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Btrfs: optimize fsync for the single writer case 



This patch optimizes the tree logging stuff so it doesn't always wait 1 jiffie
for new people to join the logging transaction if there is only ever 1 writer.
This helps a little bit with latency where we have something like RPM where it
will fdatasync every file it writes, and so waiting the 1 jiffie for every
fdatasync really starts to add up.

Signed-off-by: default avatarJosef Bacik <jbacik@redhat.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent e3ccfa98

fs/btrfs/ctree.h

+2 −0
Original line number Diff line number Diff line
@@ -1010,6 +1010,8 @@ struct btrfs_root { 
	atomic_t log_commit[2];

	unsigned long log_transid;

	unsigned long log_batch;

	pid_t log_start_pid;

	bool log_multiple_pids;



	u64 objectid;

	u64 last_trans;

fs/btrfs/tree-log.c

+11 −1
Original line number Diff line number Diff line
@@ -137,11 +137,20 @@ static int start_log_trans(struct btrfs_trans_handle *trans, 


	mutex_lock(&root->log_mutex);

	if (root->log_root) {

		if (!root->log_start_pid) {

			root->log_start_pid = current->pid;

			root->log_multiple_pids = false;

		} else if (root->log_start_pid != current->pid) {

			root->log_multiple_pids = true;

		}



		root->log_batch++;

		atomic_inc(&root->log_writers);

		mutex_unlock(&root->log_mutex);

		return 0;

	}

	root->log_multiple_pids = false;

	root->log_start_pid = current->pid;

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

	if (!root->fs_info->log_root_tree) {

		ret = btrfs_init_log_root_tree(trans, root->fs_info);
@@ -1985,7 +1994,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, 
	if (atomic_read(&root->log_commit[(index1 + 1) % 2]))

		wait_log_commit(trans, root, root->log_transid - 1);



	while (1) {

	while (root->log_multiple_pids) {

		unsigned long batch = root->log_batch;

		mutex_unlock(&root->log_mutex);

		schedule_timeout_uninterruptible(1);
@@ -2011,6 +2020,7 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, 
	root->log_batch = 0;

	root->log_transid++;

	log->log_transid = root->log_transid;

	root->log_start_pid = 0;

	smp_mb();

	/*

	 * log tree has been flushed to disk, new modifications of