jbd2: Remove t_handle_lock from start_this_handle()
This should remove the last exclusive lock from start_this_handle(),
so that we should now be able to start multiple transactions at the
same time on large SMP systems.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 6630651..0752bcd 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -57,6 +57,7 @@
spin_lock_init(&transaction->t_handle_lock);
atomic_set(&transaction->t_updates, 0);
atomic_set(&transaction->t_outstanding_credits, 0);
+ atomic_set(&transaction->t_handle_count, 0);
INIT_LIST_HEAD(&transaction->t_inode_list);
INIT_LIST_HEAD(&transaction->t_private_list);
@@ -180,8 +181,8 @@
* buffers requested by this operation, we need to stall pending a log
* checkpoint to free some more log space.
*/
- spin_lock(&transaction->t_handle_lock);
- needed = atomic_read(&transaction->t_outstanding_credits) + nblocks;
+ needed = atomic_add_return(nblocks,
+ &transaction->t_outstanding_credits);
if (needed > journal->j_max_transaction_buffers) {
/*
@@ -192,7 +193,7 @@
DEFINE_WAIT(wait);
jbd_debug(2, "Handle %p starting new commit...\n", handle);
- spin_unlock(&transaction->t_handle_lock);
+ atomic_sub(nblocks, &transaction->t_outstanding_credits);
prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
TASK_UNINTERRUPTIBLE);
__jbd2_log_start_commit(journal, transaction->t_tid);
@@ -229,7 +230,7 @@
*/
if (__jbd2_log_space_left(journal) < jbd_space_needed(journal)) {
jbd_debug(2, "Handle %p waiting for checkpoint...\n", handle);
- spin_unlock(&transaction->t_handle_lock);
+ atomic_sub(nblocks, &transaction->t_outstanding_credits);
read_unlock(&journal->j_state_lock);
write_lock(&journal->j_state_lock);
if (__jbd2_log_space_left(journal) < jbd_space_needed(journal))
@@ -239,23 +240,33 @@
}
/* OK, account for the buffers that this operation expects to
- * use and add the handle to the running transaction. */
-
- if (time_after(transaction->t_start, ts)) {
+ * use and add the handle to the running transaction.
+ *
+ * In order for t_max_wait to be reliable, it must be
+ * protected by a lock. But doing so will mean that
+ * start_this_handle() can not be run in parallel on SMP
+ * systems, which limits our scalability. So we only enable
+ * it when debugging is enabled. We may want to use a
+ * separate flag, eventually, so we can enable this
+ * independently of debugging.
+ */
+#ifdef CONFIG_JBD2_DEBUG
+ if (jbd2_journal_enable_debug &&
+ time_after(transaction->t_start, ts)) {
ts = jbd2_time_diff(ts, transaction->t_start);
+ spin_lock(&transaction->t_handle_lock);
if (ts > transaction->t_max_wait)
transaction->t_max_wait = ts;
+ spin_unlock(&transaction->t_handle_lock);
}
-
+#endif
handle->h_transaction = transaction;
- atomic_add(nblocks, &transaction->t_outstanding_credits);
atomic_inc(&transaction->t_updates);
- transaction->t_handle_count++;
+ atomic_inc(&transaction->t_handle_count);
jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
handle, nblocks,
atomic_read(&transaction->t_outstanding_credits),
__jbd2_log_space_left(journal));
- spin_unlock(&transaction->t_handle_lock);
read_unlock(&journal->j_state_lock);
lock_map_acquire(&handle->h_lockdep_map);