3 files changed, 73 insertions, 14 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 6393fd0d804..f22d1828ea8 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -355,6 +355,8 @@ void jbd2_journal_commit_transaction(journal_t *journal)
         int flags;
         int err;
         unsigned long long blocknr;
+        ktime_t start_time;
+        u64 commit_time;
         char *tagp = NULL;
         journal_header_t *header;
         journal_block_tag_t *tag = NULL;
@@ -481,6 +483,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
         commit_transaction->t_state = T_FLUSH;
         journal->j_committing_transaction = commit_transaction;
         journal->j_running_transaction = NULL;
+        start_time = ktime_get();
         commit_transaction->t_log_start = journal->j_head;
         wake_up(&journal->j_wait_transaction_locked);
         spin_unlock(&journal->j_state_lock);
@@ -995,6 +998,17 @@ restart_loop:
         J_ASSERT(commit_transaction == journal->j_committing_transaction);
         journal->j_commit_sequence = commit_transaction->t_tid;
         journal->j_committing_transaction = NULL;
+        commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
+
+        /*
+         * weight the commit time higher than the average time so we don't
+         * react too strongly to vast changes in the commit time
+         */
+        if (likely(journal->j_average_commit_time))
+                journal->j_average_commit_time = (commit_time +
+                                journal->j_average_commit_time*3) / 4;
+        else
+                journal->j_average_commit_time = commit_time;
         spin_unlock(&journal->j_state_lock);
 
         if (journal->j_commit_callback)
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 39b7805a599..13dcbc990f4 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -25,6 +25,7 @@
 #include <linux/timer.h>
 #include <linux/mm.h>
 #include <linux/highmem.h>
+#include <linux/hrtimer.h>
 
 static void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh);
 
@@ -48,6 +49,7 @@ jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
 {
         transaction->t_journal = journal;
         transaction->t_state = T_RUNNING;
+        transaction->t_start_time = ktime_get();
         transaction->t_tid = journal->j_transaction_sequence++;
         transaction->t_expires = jiffies + journal->j_commit_interval;
         spin_lock_init(&transaction->t_handle_lock);
@@ -1193,7 +1195,7 @@ int jbd2_journal_stop(handle_t *handle)
 {
         transaction_t *transaction = handle->h_transaction;
         journal_t *journal = transaction->t_journal;
-        int old_handle_count, err;
+        int err;
         pid_t pid;
 
         J_ASSERT(journal_current_handle() == handle);
@@ -1216,24 +1218,52 @@ int jbd2_journal_stop(handle_t *handle)
         /*
          * Implement synchronous transaction batching.  If the handle
          * was synchronous, don't force a commit immediately.  Let's
-         * yield and let another thread piggyback onto this transaction.
-         * Keep doing that while new threads continue to arrive.
-         * It doesn't cost much - we're about to run a commit and sleep
-         * on IO anyway.  Speeds up many-threaded, many-dir operations
-         * by 30x or more...
+         * yield and let another thread piggyback onto this
+         * transaction.  Keep doing that while new threads continue to
+         * arrive.  It doesn't cost much - we're about to run a commit
+         * and sleep on IO anyway.  Speeds up many-threaded, many-dir
+         * operations by 30x or more...
+         *
+         * We try and optimize the sleep time against what the
+         * underlying disk can do, instead of having a static sleep
+         * time.  This is useful for the case where our storage is so
+         * fast that it is more optimal to go ahead and force a flush
+         * and wait for the transaction to be committed than it is to
+         * wait for an arbitrary amount of time for new writers to
+         * join the transaction.  We achieve this by measuring how
+         * long it takes to commit a transaction, and compare it with
+         * how long this transaction has been running, and if run time
+         * < commit time then we sleep for the delta and commit.  This
+         * greatly helps super fast disks that would see slowdowns as
+         * more threads started doing fsyncs.
          *
-         * But don't do this if this process was the most recent one to
-         * perform a synchronous write.  We do this to detect the case where a
-         * single process is doing a stream of sync writes.  No point in waiting
-         * for joiners in that case.
+         * But don't do this if this process was the most recent one
+         * to perform a synchronous write.  We do this to detect the
+         * case where a single process is doing a stream of sync
+         * writes.  No point in waiting for joiners in that case.
          */
         pid = current->pid;
         if (handle->h_sync && journal->j_last_sync_writer != pid) {
+                u64 commit_time, trans_time;
+
                 journal->j_last_sync_writer = pid;
-                do {
-                        old_handle_count = transaction->t_handle_count;
-                        schedule_timeout_uninterruptible(1);
-                } while (old_handle_count != transaction->t_handle_count);
+
+                spin_lock(&journal->j_state_lock);
+                commit_time = journal->j_average_commit_time;
+                spin_unlock(&journal->j_state_lock);
+
+                trans_time = ktime_to_ns(ktime_sub(ktime_get(),
+                                                   transaction->t_start_time));
+
+                commit_time = min_t(u64, commit_time,
+                                    1000*jiffies_to_usecs(1));
+
+                if (trans_time < commit_time) {
+                        ktime_t expires = ktime_add_ns(ktime_get(),
+                                                       commit_time);
+                        set_current_state(TASK_UNINTERRUPTIBLE);
+                        schedule_hrtimeout(&expires, HRTIMER_MODE_ABS);
+                }
         }
 
         current->journal_info = NULL;
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index f3664574548..ab8cef130c2 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -638,6 +638,11 @@ struct transaction_s
         unsigned long           t_expires;
 
         /*
+         * When this transaction started, in nanoseconds [no locking]
+         */
+        ktime_t                 t_start_time;
+
+        /*
          * How many handles used this transaction? [t_handle_lock]
          */
         int t_handle_count;
@@ -939,8 +944,18 @@ struct journal_s
         struct buffer_head      **j_wbuf;
         int                     j_wbufsize;
 
+        /*
+         * this is the pid of hte last person to run a synchronous operation
+         * through the journal
+         */
         pid_t                   j_last_sync_writer;
 
+        /*
+         * the average amount of time in nanoseconds it takes to commit a
+         * transaction to disk. [j_state_lock]
+         */
+        u64                     j_average_commit_time;
+
         /* This function is called when a transaction is closed */
         void                    (*j_commit_callback)(journal_t *,
                                                      transaction_t *);