[PATCH 16/16] drbd: atomically update queue limits in drbd_reconsider_queue_parameters

[Christoph Hellwig]

Switch drbd_reconsider_queue_parameters to set up the queue parameters
in an on-stack queue_limits structure and apply the atomically.  Remove
various helpers that have become so trivial that they can be folded into
drbd_reconsider_queue_parameters.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/block/drbd/drbd_nl.c | 119 ++++++++++++++---------------------
 1 file changed, 46 insertions(+), 73 deletions(-)

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 94ed2b3ea6361d..fbd92803dc1da4 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1216,11 +1216,6 @@ static unsigned int drbd_max_peer_bio_size(struct drbd_device *device)
 	return DRBD_MAX_BIO_SIZE;
 }
 
-static void blk_queue_discard_granularity(struct request_queue *q, unsigned int granularity)
-{
-	q->limits.discard_granularity = granularity;
-}
-
 static unsigned int drbd_max_discard_sectors(struct drbd_connection *connection)
 {
 	/* when we introduced REQ_WRITE_SAME support, we also bumped
@@ -1247,62 +1242,6 @@ static bool drbd_discard_supported(struct drbd_connection *connection,
 	return true;
 }
 
-static void decide_on_discard_support(struct drbd_device *device,
-		struct drbd_backing_dev *bdev)
-{
-	struct drbd_connection *connection =
-		first_peer_device(device)->connection;
-	struct request_queue *q = device->rq_queue;
-	unsigned int max_discard_sectors;
-
-	if (!drbd_discard_supported(connection, bdev))
-		goto not_supported;
-
-	/*
-	 * We don't care for the granularity, really.
-	 *
-	 * Stacking limits below should fix it for the local device.  Whether or
-	 * not it is a suitable granularity on the remote device is not our
-	 * problem, really. If you care, you need to use devices with similar
-	 * topology on all peers.
-	 */
-	blk_queue_discard_granularity(q, 512);
-	max_discard_sectors = drbd_max_discard_sectors(connection);
-	blk_queue_max_discard_sectors(q, max_discard_sectors);
-	return;
-
-not_supported:
-	blk_queue_discard_granularity(q, 0);
-	blk_queue_max_discard_sectors(q, 0);
-}
-
-static void fixup_write_zeroes(struct drbd_device *device, struct request_queue *q)
-{
-	/* Fixup max_write_zeroes_sectors after blk_stack_limits():
-	 * if we can handle "zeroes" efficiently on the protocol,
-	 * we want to do that, even if our backend does not announce
-	 * max_write_zeroes_sectors itself. */
-	struct drbd_connection *connection = first_peer_device(device)->connection;
-	/* If the peer announces WZEROES support, use it.  Otherwise, rather
-	 * send explicit zeroes than rely on some discard-zeroes-data magic. */
-	if (connection->agreed_features & DRBD_FF_WZEROES)
-		q->limits.max_write_zeroes_sectors = DRBD_MAX_BBIO_SECTORS;
-	else
-		q->limits.max_write_zeroes_sectors = 0;
-}
-
-static void fixup_discard_support(struct drbd_device *device, struct request_queue *q)
-{
-	unsigned int max_discard = device->rq_queue->limits.max_discard_sectors;
-	unsigned int discard_granularity =
-		device->rq_queue->limits.discard_granularity >> SECTOR_SHIFT;
-
-	if (discard_granularity > max_discard) {
-		blk_queue_discard_granularity(q, 0);
-		blk_queue_max_discard_sectors(q, 0);
-	}
-}
-
 /* This is the workaround for "bio would need to, but cannot, be split" */
 static unsigned int drbd_backing_dev_max_segments(struct drbd_device *device)
 {
@@ -1320,8 +1259,11 @@ static unsigned int drbd_backing_dev_max_segments(struct drbd_device *device)
 void drbd_reconsider_queue_parameters(struct drbd_device *device,
 		struct drbd_backing_dev *bdev, struct o_qlim *o)
 {
+	struct drbd_connection *connection =
+		first_peer_device(device)->connection;
 	struct request_queue * const q = device->rq_queue;
 	unsigned int now = queue_max_hw_sectors(q) << 9;
+	struct queue_limits lim;
 	struct request_queue *b = NULL;
 	unsigned int new;
 
@@ -1348,24 +1290,55 @@ void drbd_reconsider_queue_parameters(struct drbd_device *device,
 		drbd_info(device, "max BIO size = %u\n", new);
 	}
 
+	lim = queue_limits_start_update(q);
 	if (bdev) {
-		blk_set_stacking_limits(&q->limits);
-		blk_queue_max_segments(q,
-			drbd_backing_dev_max_segments(device));
+		blk_set_stacking_limits(&lim);
+		lim.max_segments = drbd_backing_dev_max_segments(device);
 	} else {
-		blk_queue_max_segments(q, BLK_MAX_SEGMENTS);
+		lim.max_segments = BLK_MAX_SEGMENTS;
 	}
 
-	blk_queue_max_hw_sectors(q, new >> SECTOR_SHIFT);
-	blk_queue_segment_boundary(q, PAGE_SIZE - 1);
-	decide_on_discard_support(device, bdev);
+	lim.max_hw_sectors = new >> SECTOR_SHIFT;
+	lim.seg_boundary_mask = PAGE_SIZE - 1;
 
-	if (bdev) {
-		blk_stack_limits(&q->limits, &b->limits, 0);
-		disk_update_readahead(device->vdisk);
+	/*
+	 * We don't care for the granularity, really.
+	 *
+	 * Stacking limits below should fix it for the local device.  Whether or
+	 * not it is a suitable granularity on the remote device is not our
+	 * problem, really. If you care, you need to use devices with similar
+	 * topology on all peers.
+	 */
+	if (drbd_discard_supported(connection, bdev)) {
+		lim.discard_granularity = 512;
+		lim.max_hw_discard_sectors =
+			drbd_max_discard_sectors(connection);
+	} else {
+		lim.discard_granularity = 0;
+		lim.max_hw_discard_sectors = 0;
 	}
-	fixup_write_zeroes(device, q);
-	fixup_discard_support(device, q);
+
+	if (bdev)
+		blk_stack_limits(&lim, &b->limits, 0);
+
+	/*
+	 * If we can handle "zeroes" efficiently on the protocol, we want to do
+	 * that, even if our backend does not announce max_write_zeroes_sectors
+	 * itself.
+	 */
+	if (connection->agreed_features & DRBD_FF_WZEROES)
+		lim.max_write_zeroes_sectors = DRBD_MAX_BBIO_SECTORS;
+	else
+		lim.max_write_zeroes_sectors = 0;
+
+	if ((lim.discard_granularity >> SECTOR_SHIFT) >
+	    lim.max_hw_discard_sectors) {
+		lim.discard_granularity = 0;
+		lim.max_hw_discard_sectors = 0;
+	}
+
+	if (queue_limits_commit_update(q, &lim))
+		drbd_err(device, "setting new queue limits failed\n");
 }
 
 /* Starts the worker thread */
-- 
2.39.2