linux-kernel - [PATCH 1/2] md/bitmap: Move unplug to daemon thread

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Date:   Thu,  6 Oct 2022 16:08:39 -0600
From:   Jonathan Derrick <jonathan.derrick@...ux.dev>
To:     Song Liu <song@...nel.org>
Cc:     <linux-raid@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        jonathan.derrick@...idigm.com, jonathanx.sk.derrick@...el.com,
        Jonathan Derrick <jonathan.derrick@...ux.dev>
Subject: [PATCH 1/2] md/bitmap: Move unplug to daemon thread

It's been observed in raid1/raid10 configurations that synchronous I/O
can cause workloads resulting in greater than 40% bitmap updates. This
appears to be due to the synchronous workload requiring a bitmap flush
with every flush of the I/O list. Instead prefer to flush this
configuration in the daemon sleeper thread.

Signed-off-by: Jonathan Derrick <jonathan.derrick@...ux.dev>
---
 drivers/md/md-bitmap.c | 1 +
 drivers/md/raid1.c     | 2 --
 drivers/md/raid10.c    | 4 ----
 3 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index bf6dffadbe6f..451259b38d25 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1244,6 +1244,7 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 			+ mddev->bitmap_info.daemon_sleep))
 		goto done;
 
+	md_bitmap_unplug(bitmap);
 	bitmap->daemon_lastrun = jiffies;
 	if (bitmap->allclean) {
 		mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 05d8438cfec8..42ba2d884773 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -793,8 +793,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 
 static void flush_bio_list(struct r1conf *conf, struct bio *bio)
 {
-	/* flush any pending bitmap writes to disk before proceeding w/ I/O */
-	md_bitmap_unplug(conf->mddev->bitmap);
 	wake_up(&conf->wait_barrier);
 
 	while (bio) { /* submit pending writes */
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 9117fcdee1be..e43352aae3c4 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -881,9 +881,6 @@ static void flush_pending_writes(struct r10conf *conf)
 		__set_current_state(TASK_RUNNING);
 
 		blk_start_plug(&plug);
-		/* flush any pending bitmap writes to disk
-		 * before proceeding w/ I/O */
-		md_bitmap_unplug(conf->mddev->bitmap);
 		wake_up(&conf->wait_barrier);
 
 		while (bio) { /* submit pending writes */
@@ -1078,7 +1075,6 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
 
 	/* we aren't scheduling, so we can do the write-out directly. */
 	bio = bio_list_get(&plug->pending);
-	md_bitmap_unplug(mddev->bitmap);
 	wake_up(&conf->wait_barrier);
 
 	while (bio) { /* submit pending writes */
-- 
2.31.1