GFS2: introduce AIL lock

The log lock is currently used to protect the AIL lists and
the movements of buffers into and out of them. The lists
are self contained and no log specific items outside the
lists are accessed when starting or emptying the AIL lists.

Hence the operation of the AIL does not require the protection
of the log lock so split them out into a new AIL specific lock
to reduce the amount of traffic on the log lock. This will
also reduce the amount of serialisation that occurs when
the gfs2_logd pushes on the AIL to move it forward.

This reduces the impact of log pushing on sequential write
throughput.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 16 insertions, 14 deletions

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index eb01f3575e1..4e3c044934e 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -88,8 +88,8 @@ void gfs2_remove_from_ail(struct gfs2_bufdata *bd)
  */
 
 static void gfs2_ail1_start_one(struct gfs2_sbd *sdp, struct gfs2_ail *ai)
-__releases(&sdp->sd_log_lock)
-__acquires(&sdp->sd_log_lock)
+__releases(&sdp->sd_ail_lock)
+__acquires(&sdp->sd_ail_lock)
 {
 	struct gfs2_bufdata *bd, *s;
 	struct buffer_head *bh;
@@ -117,7 +117,7 @@ __acquires(&sdp->sd_log_lock)
 			list_move(&bd->bd_ail_st_list, &ai->ai_ail1_list);
 
 			get_bh(bh);
-			gfs2_log_unlock(sdp);
+			spin_unlock(&sdp->sd_ail_lock);
 			lock_buffer(bh);
 			if (test_clear_buffer_dirty(bh)) {
 				bh->b_end_io = end_buffer_write_sync;
@@ -126,7 +126,7 @@ __acquires(&sdp->sd_log_lock)
 				unlock_buffer(bh);
 				brelse(bh);
 			}
-			gfs2_log_lock(sdp);
+			spin_lock(&sdp->sd_ail_lock);
 
 			retry = 1;
 			break;
@@ -175,10 +175,10 @@ static void gfs2_ail1_start(struct gfs2_sbd *sdp)
 	struct gfs2_ail *ai;
 	int done = 0;
 
-	gfs2_log_lock(sdp);
+	spin_lock(&sdp->sd_ail_lock);
 	head = &sdp->sd_ail1_list;
 	if (list_empty(head)) {
-		gfs2_log_unlock(sdp);
+		spin_unlock(&sdp->sd_ail_lock);
 		return;
 	}
 	sync_gen = sdp->sd_ail_sync_gen++;
@@ -189,13 +189,13 @@ static void gfs2_ail1_start(struct gfs2_sbd *sdp)
 			if (ai->ai_sync_gen >= sync_gen)
 				continue;
 			ai->ai_sync_gen = sync_gen;
-			gfs2_ail1_start_one(sdp, ai); /* This may drop log lock */
+			gfs2_ail1_start_one(sdp, ai); /* This may drop ail lock */
 			done = 0;
 			break;
 		}
 	}
 
-	gfs2_log_unlock(sdp);
+	spin_unlock(&sdp->sd_ail_lock);
 }
 
 static int gfs2_ail1_empty(struct gfs2_sbd *sdp, int flags)
@@ -203,7 +203,7 @@ static int gfs2_ail1_empty(struct gfs2_sbd *sdp, int flags)
 	struct gfs2_ail *ai, *s;
 	int ret;
 
-	gfs2_log_lock(sdp);
+	spin_lock(&sdp->sd_ail_lock);
 
 	list_for_each_entry_safe_reverse(ai, s, &sdp->sd_ail1_list, ai_list) {
 		if (gfs2_ail1_empty_one(sdp, ai, flags))
@@ -214,7 +214,7 @@ static int gfs2_ail1_empty(struct gfs2_sbd *sdp, int flags)
 
 	ret = list_empty(&sdp->sd_ail1_list);
 
-	gfs2_log_unlock(sdp);
+	spin_unlock(&sdp->sd_ail_lock);
 
 	return ret;
 }
@@ -247,7 +247,7 @@ static void ail2_empty(struct gfs2_sbd *sdp, unsigned int new_tail)
 	int wrap = (new_tail < old_tail);
 	int a, b, rm;
 
-	gfs2_log_lock(sdp);
+	spin_lock(&sdp->sd_ail_lock);
 
 	list_for_each_entry_safe(ai, safe, &sdp->sd_ail2_list, ai_list) {
 		a = (old_tail <= ai->ai_first);
@@ -263,7 +263,7 @@ static void ail2_empty(struct gfs2_sbd *sdp, unsigned int new_tail)
 		kfree(ai);
 	}
 
-	gfs2_log_unlock(sdp);
+	spin_unlock(&sdp->sd_ail_lock);
 }
 
 /**
@@ -421,7 +421,7 @@ static unsigned int current_tail(struct gfs2_sbd *sdp)
 	struct gfs2_ail *ai;
 	unsigned int tail;
 
-	gfs2_log_lock(sdp);
+	spin_lock(&sdp->sd_ail_lock);
 
 	if (list_empty(&sdp->sd_ail1_list)) {
 		tail = sdp->sd_log_head;
@@ -430,7 +430,7 @@ static unsigned int current_tail(struct gfs2_sbd *sdp)
 		tail = ai->ai_first;
 	}
 
-	gfs2_log_unlock(sdp);
+	spin_unlock(&sdp->sd_ail_lock);
 
 	return tail;
 }
@@ -743,10 +743,12 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl)
 	sdp->sd_log_commited_databuf = 0;
 	sdp->sd_log_commited_revoke = 0;
 
+	spin_lock(&sdp->sd_ail_lock);
 	if (!list_empty(&ai->ai_ail1_list)) {
 		list_add(&ai->ai_list, &sdp->sd_ail1_list);
 		ai = NULL;
 	}
+	spin_unlock(&sdp->sd_ail_lock);
 	gfs2_log_unlock(sdp);
 	trace_gfs2_log_flush(sdp, 0);
 	up_write(&sdp->sd_log_flush_lock);