jbd2: use WRITE_SYNC_PLUG instead of WRITE_SYNC

When you are going to be submitting several sync writes, we want to
give the IO scheduler a chance to merge some of them. Instead of
using the implicitly unplugging WRITE_SYNC variant, use WRITE_SYNC_PLUG
and rely on sync_buffer() doing the unplug when someone does a
wait_on_buffer()/lock_buffer().

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 4 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 4ea72377c7a2..073c8c3df7cd 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -138,7 +138,7 @@ static int journal_submit_commit_record(journal_t *journal,
                 set_buffer_ordered(bh);
                 barrier_done = 1;
         }
-        ret = submit_bh(WRITE_SYNC, bh);
+        ret = submit_bh(WRITE_SYNC_PLUG, bh);
         if (barrier_done)
                 clear_buffer_ordered(bh);
 
@@ -159,7 +159,7 @@ static int journal_submit_commit_record(journal_t *journal,
                 lock_buffer(bh);
                 set_buffer_uptodate(bh);
                 clear_buffer_dirty(bh);
-                ret = submit_bh(WRITE_SYNC, bh);
+                ret = submit_bh(WRITE_SYNC_PLUG, bh);
         }
         *cbh = bh;
         return ret;
@@ -190,7 +190,7 @@ retry:
                 set_buffer_uptodate(bh);
                 bh->b_end_io = journal_end_buffer_io_sync;
 
-                ret = submit_bh(WRITE_SYNC, bh);
+                ret = submit_bh(WRITE_SYNC_PLUG, bh);
                 if (ret) {
                         unlock_buffer(bh);
                         return ret;
@@ -402,8 +402,13 @@ void jbd2_journal_commit_transaction(journal_t *journal)
         spin_lock(&journal->j_state_lock);
         commit_transaction->t_state = T_LOCKED;
 
+        /*
+         * Use plugged writes here, since we want to submit several before
+         * we unplug the device. We don't do explicit unplugging in here,
+         * instead we rely on sync_buffer() doing the unplug for us.
+         */
         if (commit_transaction->t_synchronous_commit)
-                write_op = WRITE_SYNC;
+                write_op = WRITE_SYNC_PLUG;
         stats.u.run.rs_wait = commit_transaction->t_max_wait;
         stats.u.run.rs_locked = jiffies;
         stats.u.run.rs_running = jbd2_time_diff(commit_transaction->t_start,