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/commit.c b/fs/jbd2/commit.c
index 67bb0a2f35e5f0feacb4ef01757b18b793e457a8..f52e5e8049f195ec461bfb8781584722b5da2562 100644 (file)
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -1004,7 +1004,8 @@ restart_loop:
         * File the transaction statistics
         */
        stats.ts_tid = commit_transaction->t_tid;
-       stats.run.rs_handle_count = commit_transaction->t_handle_count;
+       stats.run.rs_handle_count =
+               atomic_read(&commit_transaction->t_handle_count);
        trace_jbd2_run_stats(journal->j_fs_dev->bd_dev,
                             commit_transaction->t_tid, &stats.run);
 

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 663065142b4245910583c1a33d282af53fe03f37..0752bcda535f544425a49bad62785ec3d7689c96 100644 (file)
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -57,6 +57,7 @@ jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
        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 @@ repeat:
         * 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 @@ repeat:
                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 @@ repeat:
         */
        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 @@ repeat:
        }
 
        /* 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);

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 15d5743ccfbb86a1f427d067a262411072562e58..01743b5446ffec82b8837873eaae0774ad46c28a 100644 (file)
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -629,7 +629,7 @@ struct transaction_s
        /*
         * How many handles used this transaction? [t_handle_lock]
         */
-       int t_handle_count;
+       atomic_t                t_handle_count;
 
        /*
         * This transaction is being forced and some process is