[PATCH 2/4] md: add a new api sync_io_depth

[Yu Kuai <yukuai1@huaweicloud.com>]

From: Yu Kuai <yukuai3@huawei.com>

Currently if sync speed is above speed_min and below speed_max,
md_do_sync() will wait for all sync IOs to be done before issuing new
sync IO, means sync IO depth is limited to just 1.

This limit is too low, in order to prevent sync speed drop conspicuously
after fixing is_mddev_idle() in the next patch, add a new api for
limiting sync IO depth, the default value is 32.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 103 +++++++++++++++++++++++++++++++++++++++---------
 drivers/md/md.h |   1 +
 2 files changed, 85 insertions(+), 19 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 438e71e45c16..8966c4afc62a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -111,32 +111,42 @@ static void md_wakeup_thread_directly(struct md_thread __rcu *thread);
 /* Default safemode delay: 200 msec */
 #define DEFAULT_SAFEMODE_DELAY ((200 * HZ)/1000 +1)
 /*
- * Current RAID-1,4,5 parallel reconstruction 'guaranteed speed limit'
- * is 1000 KB/sec, so the extra system load does not show up that much.
- * Increase it if you want to have more _guaranteed_ speed. Note that
- * the RAID driver will use the maximum available bandwidth if the IO
- * subsystem is idle. There is also an 'absolute maximum' reconstruction
- * speed limit - in case reconstruction slows down your system despite
- * idle IO detection.
+ * Background sync IO speed control:
  *
- * you can change it via /proc/sys/dev/raid/speed_limit_min and _max.
- * or /sys/block/mdX/md/sync_speed_{min,max}
+ * - below speed min:
+ *   no limit;
+ * - above speed min and below speed max:
+ *   a) if mddev is idle, then no limit;
+ *   b) if mddev is busy handling normal IO, then limit inflight sync IO
+ *   to sync_io_depth;
+ * - above speed max:
+ *   sync IO can't be issued;
+ *
+ * Following configurations can be changed via /proc/sys/dev/raid/ for system
+ * or /sys/block/mdX/md/ for one array.
  */
-
 static int sysctl_speed_limit_min = 1000;
 static int sysctl_speed_limit_max = 200000;
-static inline int speed_min(struct mddev *mddev)
+static int sysctl_sync_io_depth = 32;
+
+static int speed_min(struct mddev *mddev)
 {
 	return mddev->sync_speed_min ?
 		mddev->sync_speed_min : sysctl_speed_limit_min;
 }
 
-static inline int speed_max(struct mddev *mddev)
+static int speed_max(struct mddev *mddev)
 {
 	return mddev->sync_speed_max ?
 		mddev->sync_speed_max : sysctl_speed_limit_max;
 }
 
+static int sync_io_depth(struct mddev *mddev)
+{
+	return mddev->sync_io_depth ?
+		mddev->sync_io_depth : sysctl_sync_io_depth;
+}
+
 static void rdev_uninit_serial(struct md_rdev *rdev)
 {
 	if (!test_and_clear_bit(CollisionCheck, &rdev->flags))
@@ -293,14 +303,21 @@ static const struct ctl_table raid_table[] = {
 		.procname	= "speed_limit_min",
 		.data		= &sysctl_speed_limit_min,
 		.maxlen		= sizeof(int),
-		.mode		= S_IRUGO|S_IWUSR,
+		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
 	{
 		.procname	= "speed_limit_max",
 		.data		= &sysctl_speed_limit_max,
 		.maxlen		= sizeof(int),
-		.mode		= S_IRUGO|S_IWUSR,
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+	{
+		.procname	= "sync_io_depth",
+		.data		= &sysctl_sync_io_depth,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
 };
@@ -5091,7 +5108,7 @@ static ssize_t
 sync_min_show(struct mddev *mddev, char *page)
 {
 	return sprintf(page, "%d (%s)\n", speed_min(mddev),
-		       mddev->sync_speed_min ? "local": "system");
+		       mddev->sync_speed_min ? "local" : "system");
 }
 
 static ssize_t
@@ -5100,7 +5117,7 @@ sync_min_store(struct mddev *mddev, const char *buf, size_t len)
 	unsigned int min;
 	int rv;
 
-	if (strncmp(buf, "system", 6)==0) {
+	if (strncmp(buf, "system", 6) == 0) {
 		min = 0;
 	} else {
 		rv = kstrtouint(buf, 10, &min);
@@ -5120,7 +5137,7 @@ static ssize_t
 sync_max_show(struct mddev *mddev, char *page)
 {
 	return sprintf(page, "%d (%s)\n", speed_max(mddev),
-		       mddev->sync_speed_max ? "local": "system");
+		       mddev->sync_speed_max ? "local" : "system");
 }
 
 static ssize_t
@@ -5129,7 +5146,7 @@ sync_max_store(struct mddev *mddev, const char *buf, size_t len)
 	unsigned int max;
 	int rv;
 
-	if (strncmp(buf, "system", 6)==0) {
+	if (strncmp(buf, "system", 6) == 0) {
 		max = 0;
 	} else {
 		rv = kstrtouint(buf, 10, &max);
@@ -5145,6 +5162,35 @@ sync_max_store(struct mddev *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry md_sync_max =
 __ATTR(sync_speed_max, S_IRUGO|S_IWUSR, sync_max_show, sync_max_store);
 
+static ssize_t
+sync_io_depth_show(struct mddev *mddev, char *page)
+{
+	return sprintf(page, "%d (%s)\n", sync_io_depth(mddev),
+		       mddev->sync_io_depth ? "local" : "system");
+}
+
+static ssize_t
+sync_io_depth_store(struct mddev *mddev, const char *buf, size_t len)
+{
+	unsigned int max;
+	int rv;
+
+	if (strncmp(buf, "system", 6) == 0) {
+		max = 0;
+	} else {
+		rv = kstrtouint(buf, 10, &max);
+		if (rv < 0)
+			return rv;
+		if (max == 0)
+			return -EINVAL;
+	}
+	mddev->sync_io_depth = max;
+	return len;
+}
+
+static struct md_sysfs_entry md_sync_io_depth =
+__ATTR_RW(sync_io_depth);
+
 static ssize_t
 degraded_show(struct mddev *mddev, char *page)
 {
@@ -5671,6 +5717,7 @@ static struct attribute *md_redundancy_attrs[] = {
 	&md_mismatches.attr,
 	&md_sync_min.attr,
 	&md_sync_max.attr,
+	&md_sync_io_depth.attr,
 	&md_sync_speed.attr,
 	&md_sync_force_parallel.attr,
 	&md_sync_completed.attr,
@@ -8927,6 +8974,23 @@ static sector_t md_sync_position(struct mddev *mddev, enum sync_action action)
 	}
 }
 
+static bool sync_io_within_limit(struct mddev *mddev)
+{
+	int io_sectors;
+
+	/*
+	 * For raid456, sync IO is stripe(4k) per IO, for other levels, it's
+	 * RESYNC_PAGES(64k) per IO.
+	 */
+	if (mddev->level == 4 || mddev->level == 5 || mddev->level == 6)
+		io_sectors = 8;
+	else
+		io_sectors = 128;
+
+	return atomic_read(&mddev->recovery_active) <
+		io_sectors * sync_io_depth(mddev);
+}
+
 #define SYNC_MARKS	10
 #define	SYNC_MARK_STEP	(3*HZ)
 #define UPDATE_FREQUENCY (5*60*HZ)
@@ -9195,7 +9259,8 @@ void md_do_sync(struct md_thread *thread)
 				msleep(500);
 				goto repeat;
 			}
-			if (!is_mddev_idle(mddev, 0)) {
+			if (!sync_io_within_limit(mddev) &&
+			    !is_mddev_idle(mddev, 0)) {
 				/*
 				 * Give other IO more of a chance.
 				 * The faster the devices, the less we wait.
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 1cf00a04bcdd..63be622467c6 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -483,6 +483,7 @@ struct mddev {
 	/* if zero, use the system-wide default */
 	int				sync_speed_min;
 	int				sync_speed_max;
+	int				sync_io_depth;
 
 	/* resync even though the same disks are shared among md-devices */
 	int				parallel_resync;
-- 
2.39.2