Commit ff782e0a authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
Browse files

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
......@@ -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;
......
......@@ -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
......
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