From 828cbe989e4f5c8666cb3d99918b03666ccde0a0 Mon Sep 17 00:00:00 2001
From: Shaohua Li <shli@fb.com>
Date: Wed, 2 Sep 2015 13:49:49 -0700
Subject: [PATCH] raid5-cache: optimize FLUSH IO with log enabled

With log enabled, bio is written to raid disks after the bio is settled
down in log disk. The recovery guarantees we can recovery the bio data
from log disk, so we we skip FLUSH IO.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>
---
 drivers/md/raid5-cache.c | 18 ++++++++++++++++++
 drivers/md/raid5.c       | 11 +++++++++--
 drivers/md/raid5.h       |  1 +
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 6479f15a5434..ea1480392eba 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -507,6 +507,24 @@ void r5l_write_stripe_run(struct r5l_log *log)
 	mutex_unlock(&log->io_mutex);
 }
 
+int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio)
+{
+	if (!log)
+		return -ENODEV;
+	/*
+	 * we flush log disk cache first, then write stripe data to raid disks.
+	 * So if bio is finished, the log disk cache is flushed already. The
+	 * recovery guarantees we can recovery the bio from log disk, so we
+	 * don't need to flush again
+	 */
+	if (bio->bi_iter.bi_size == 0) {
+		bio_endio(bio);
+		return 0;
+	}
+	bio->bi_rw &= ~REQ_FLUSH;
+	return -EAGAIN;
+}
+
 /* This will run after log space is reclaimed */
 static void r5l_run_no_space_stripes(struct r5l_log *log)
 {
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 46042c7c25a5..a622ccb3477a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5146,8 +5146,15 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 	bool do_prepare;
 
 	if (unlikely(bi->bi_rw & REQ_FLUSH)) {
-		md_flush_request(mddev, bi);
-		return;
+		int ret = r5l_handle_flush_request(conf->log, bi);
+
+		if (ret == 0)
+			return;
+		if (ret == -ENODEV) {
+			md_flush_request(mddev, bi);
+			return;
+		}
+		/* ret == -EAGAIN, fallback */
 	}
 
 	md_write_start(mddev, bi);
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 1f16d437bfda..32c8ce81248b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -629,4 +629,5 @@ extern int r5l_write_stripe(struct r5l_log *log, struct stripe_head *head_sh);
 extern void r5l_write_stripe_run(struct r5l_log *log);
 extern void r5l_flush_stripe_to_raid(struct r5l_log *log);
 extern void r5l_stripe_write_finished(struct stripe_head *sh);
+extern int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio);
 #endif
-- 
2.20.1