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From:   Pankaj Gupta <pankaj.gupta.linux@gmail.com>
To:     song@kernel.org
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        pankaj.gupta.linux@gmail.com,
        Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Subject: [PATCH 2/3] md: add comments in md_flush_request()
Date:   Wed, 11 Nov 2020 06:16:57 +0100
Message-Id: <20201111051658.18904-3-pankaj.gupta.linux@gmail.com>
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From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>

 Request coalescing logic is dependent on flush time
 update in other context. This patch adds comments
 to understand the code flow better.

Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
---
 drivers/md/md.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 167c80f98533..a330e61876e0 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -662,10 +662,14 @@ bool md_flush_request(struct mddev *mddev, struct bio *bio)
 {
 	ktime_t req_start = ktime_get_boottime();
 	spin_lock_irq(&mddev->lock);
+	/* flush requests wait until ongoing flush completes,
+	 * hence coalescing all the pending requests.
+	 */
 	wait_event_lock_irq(mddev->sb_wait,
 			    !mddev->flush_bio ||
 			    ktime_after(mddev->prev_flush_start, req_start),
 			    mddev->lock);
+	/* new request after previous flush is completed */
 	if (!ktime_after(mddev->prev_flush_start, req_start)) {
 		WARN_ON(mddev->flush_bio);
 		mddev->flush_bio = bio;
-- 
2.20.1