support for multi-range discard requests V3

support for multi-range discard requests V3

[Christoph Hellwig]

Hi all,

this series adds support for merging discontiguous discard bios into a
single request if the driver supports it.  This reduces the number of
discards sent to the device by about a factor of 5-6 for typical
workloads on NVMe, and for slower devices that use I/O scheduling
the number will probably be even bigger but I've not implemented
that support yet.

Changes since V2:
  - really fix nr of NVMe ranges to 256
  - free range on error

Changes since V1:
  - hardcoded max ranges for NVMe to 255
  - minor cleanups

support for multi-range discard requests V3

[Christoph Hellwig]

Hi all,

this series adds support for merging discontiguous discard bios into a
single request if the driver supports it.  This reduces the number of
discards sent to the device by about a factor of 5-6 for typical
workloads on NVMe, and for slower devices that use I/O scheduling
the number will probably be even bigger but I've not implemented
that support yet.

Changes since V2:
  - really fix nr of NVMe ranges to 256
  - free range on error

Changes since V1:
  - hardcoded max ranges for NVMe to 255
  - minor cleanups

[PATCH 1/4] block: move req_set_nomerge to blk.h

[Christoph Hellwig]

This makes it available outside of blk-merge.c, and inlining such a trivial
helper seems pretty useful to start with.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-merge.c | 7 -------
 block/blk.h       | 7 +++++++
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index a373416dbc9a..c956d9e7aafd 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -482,13 +482,6 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 }
 EXPORT_SYMBOL(blk_rq_map_sg);
 
-static void req_set_nomerge(struct request_queue *q, struct request *req)
-{
-	req->cmd_flags |= REQ_NOMERGE;
-	if (req == q->last_merge)
-		q->last_merge = NULL;
-}
-
 static inline int ll_new_hw_segment(struct request_queue *q,
 				    struct request *req,
 				    struct bio *bio)
diff --git a/block/blk.h b/block/blk.h
index 4972b98d47e1..3e08703902a9 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -256,6 +256,13 @@ static inline int blk_do_io_stat(struct request *rq)
 		!blk_rq_is_passthrough(rq);
 }
 
+static inline void req_set_nomerge(struct request_queue *q, struct request *req)
+{
+	req->cmd_flags |= REQ_NOMERGE;
+	if (req == q->last_merge)
+		q->last_merge = NULL;
+}
+
 /*
  * Internal io_context interface
  */
-- 
2.11.0

[PATCH 1/4] block: move req_set_nomerge to blk.h

[Christoph Hellwig]

This makes it available outside of blk-merge.c, and inlining such a trivial
helper seems pretty useful to start with.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-merge.c | 7 -------
 block/blk.h       | 7 +++++++
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index a373416dbc9a..c956d9e7aafd 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -482,13 +482,6 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 }
 EXPORT_SYMBOL(blk_rq_map_sg);
 
-static void req_set_nomerge(struct request_queue *q, struct request *req)
-{
-	req->cmd_flags |= REQ_NOMERGE;
-	if (req == q->last_merge)
-		q->last_merge = NULL;
-}
-
 static inline int ll_new_hw_segment(struct request_queue *q,
 				    struct request *req,
 				    struct bio *bio)
diff --git a/block/blk.h b/block/blk.h
index 4972b98d47e1..3e08703902a9 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -256,6 +256,13 @@ static inline int blk_do_io_stat(struct request *rq)
 		!blk_rq_is_passthrough(rq);
 }
 
+static inline void req_set_nomerge(struct request_queue *q, struct request *req)
+{
+	req->cmd_flags |= REQ_NOMERGE;
+	if (req == q->last_merge)
+		q->last_merge = NULL;
+}
+
 /*
  * Internal io_context interface
  */
-- 
2.11.0

[PATCH 2/4] block: enumify ELEVATOR_*_MERGE

[Christoph Hellwig]

Switch these constants to an enum, and make let the compiler ensure that
all callers of blk_try_merge and elv_merge handle all potential values.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-core.c         | 76 +++++++++++++++++++++++++-----------------------
 block/blk-merge.c        |  2 +-
 block/blk-mq-sched.c     | 35 +++++++++++-----------
 block/blk-mq.c           | 32 +++++++++-----------
 block/blk.h              |  2 +-
 block/cfq-iosched.c      |  4 +--
 block/deadline-iosched.c | 12 +++-----
 block/elevator.c         | 10 ++++---
 block/mq-deadline.c      |  2 +-
 include/linux/elevator.h | 28 ++++++++++--------
 10 files changed, 102 insertions(+), 101 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index d161d4ab7052..75fe534861df 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1513,12 +1513,11 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 {
 	struct blk_plug *plug;
 	struct request *rq;
-	bool ret = false;
 	struct list_head *plug_list;
 
 	plug = current->plug;
 	if (!plug)
-		goto out;
+		return false;
 	*request_count = 0;
 
 	if (q->mq_ops)
@@ -1527,7 +1526,7 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		plug_list = &plug->list;
 
 	list_for_each_entry_reverse(rq, plug_list, queuelist) {
-		int el_ret;
+		bool merged = false;
 
 		if (rq->q == q) {
 			(*request_count)++;
@@ -1543,19 +1542,22 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		if (rq->q != q || !blk_rq_merge_ok(rq, bio))
 			continue;
 
-		el_ret = blk_try_merge(rq, bio);
-		if (el_ret == ELEVATOR_BACK_MERGE) {
-			ret = bio_attempt_back_merge(q, rq, bio);
-			if (ret)
-				break;
-		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-			ret = bio_attempt_front_merge(q, rq, bio);
-			if (ret)
-				break;
+		switch (blk_try_merge(rq, bio)) {
+		case ELEVATOR_BACK_MERGE:
+			merged = bio_attempt_back_merge(q, rq, bio);
+			break;
+		case ELEVATOR_FRONT_MERGE:
+			merged = bio_attempt_front_merge(q, rq, bio);
+			break;
+		default:
+			break;
 		}
+
+		if (merged)
+			return true;
 	}
-out:
-	return ret;
+
+	return false;
 }
 
 unsigned int blk_plug_queued_count(struct request_queue *q)
@@ -1597,7 +1599,7 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 {
 	struct blk_plug *plug;
-	int el_ret, where = ELEVATOR_INSERT_SORT;
+	int where = ELEVATOR_INSERT_SORT;
 	struct request *req, *free;
 	unsigned int request_count = 0;
 	unsigned int wb_acct;
@@ -1635,27 +1637,29 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 
 	spin_lock_irq(q->queue_lock);
 
-	el_ret = elv_merge(q, &req, bio);
-	if (el_ret == ELEVATOR_BACK_MERGE) {
-		if (bio_attempt_back_merge(q, req, bio)) {
-			elv_bio_merged(q, req, bio);
-			free = attempt_back_merge(q, req);
-			if (!free)
-				elv_merged_request(q, req, el_ret);
-			else
-				__blk_put_request(q, free);
-			goto out_unlock;
-		}
-	} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-		if (bio_attempt_front_merge(q, req, bio)) {
-			elv_bio_merged(q, req, bio);
-			free = attempt_front_merge(q, req);
-			if (!free)
-				elv_merged_request(q, req, el_ret);
-			else
-				__blk_put_request(q, free);
-			goto out_unlock;
-		}
+	switch (elv_merge(q, &req, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		if (!bio_attempt_back_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_back_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_BACK_MERGE);
+		goto out_unlock;
+	case ELEVATOR_FRONT_MERGE:
+		if (!bio_attempt_front_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_front_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_FRONT_MERGE);
+		goto out_unlock;
+	default:
+		break;
 	}
 
 get_rq:
diff --git a/block/blk-merge.c b/block/blk-merge.c
index c956d9e7aafd..6cbd90ad5f90 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -801,7 +801,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 	return true;
 }
 
-int blk_try_merge(struct request *rq, struct bio *bio)
+enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 {
 	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 		return ELEVATOR_BACK_MERGE;
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ee455e7cf9d8..72d0d8361175 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -238,30 +238,29 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 			    struct request **merged_request)
 {
 	struct request *rq;
-	int ret;
 
-	ret = elv_merge(q, &rq, bio);
-	if (ret == ELEVATOR_BACK_MERGE) {
+	switch (elv_merge(q, &rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_back_merge(q, rq, bio)) {
-			*merged_request = attempt_back_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
-	} else if (ret == ELEVATOR_FRONT_MERGE) {
+		if (!bio_attempt_back_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_back_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
+		return true;
+	case ELEVATOR_FRONT_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_front_merge(q, rq, bio)) {
-			*merged_request = attempt_front_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
+		if (!bio_attempt_front_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_front_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
+		return true;
+	default:
+		return false;
 	}
-
-	return false;
 }
 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index be183e6115a1..9294633759d9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -763,7 +763,7 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 	int checked = 8;
 
 	list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
-		int el_ret;
+		bool merged = false;
 
 		if (!checked--)
 			break;
@@ -771,26 +771,22 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 		if (!blk_rq_merge_ok(rq, bio))
 			continue;
 
-		el_ret = blk_try_merge(rq, bio);
-		if (el_ret == ELEVATOR_NO_MERGE)
-			continue;
-
-		if (!blk_mq_sched_allow_merge(q, rq, bio))
+		switch (blk_try_merge(rq, bio)) {
+		case ELEVATOR_BACK_MERGE:
+			if (blk_mq_sched_allow_merge(q, rq, bio))
+				merged = bio_attempt_back_merge(q, rq, bio);
 			break;
-
-		if (el_ret == ELEVATOR_BACK_MERGE) {
-			if (bio_attempt_back_merge(q, rq, bio)) {
-				ctx->rq_merged++;
-				return true;
-			}
-			break;
-		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-			if (bio_attempt_front_merge(q, rq, bio)) {
-				ctx->rq_merged++;
-				return true;
-			}
+		case ELEVATOR_FRONT_MERGE:
+			if (blk_mq_sched_allow_merge(q, rq, bio))
+				merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		default:
+			continue;
 		}
+
+		if (merged)
+			ctx->rq_merged++;
+		return merged;
 	}
 
 	return false;
diff --git a/block/blk.h b/block/blk.h
index 3e08703902a9..ae82f2ac4019 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -215,7 +215,7 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 void blk_recalc_rq_segments(struct request *rq);
 void blk_rq_set_mixed_merge(struct request *rq);
 bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
-int blk_try_merge(struct request *rq, struct bio *bio);
+enum elv_merge blk_try_merge(struct request *rq, struct bio *bio);
 
 void blk_queue_congestion_threshold(struct request_queue *q);
 
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f0f29ee731e1..921262770636 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2528,7 +2528,7 @@ static void cfq_remove_request(struct request *rq)
 	}
 }
 
-static int cfq_merge(struct request_queue *q, struct request **req,
+static enum elv_merge cfq_merge(struct request_queue *q, struct request **req,
 		     struct bio *bio)
 {
 	struct cfq_data *cfqd = q->elevator->elevator_data;
@@ -2544,7 +2544,7 @@ static int cfq_merge(struct request_queue *q, struct request **req,
 }
 
 static void cfq_merged_request(struct request_queue *q, struct request *req,
-			       int type)
+			       enum elv_merge type)
 {
 	if (type == ELEVATOR_FRONT_MERGE) {
 		struct cfq_queue *cfqq = RQ_CFQQ(req);
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 05fc0ea25a98..c68f6bbc0dcd 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -120,12 +120,11 @@ static void deadline_remove_request(struct request_queue *q, struct request *rq)
 	deadline_del_rq_rb(dd, rq);
 }
 
-static int
+static enum elv_merge
 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 	struct request *__rq;
-	int ret;
 
 	/*
 	 * check for front merge
@@ -138,20 +137,17 @@ deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
 			BUG_ON(sector != blk_rq_pos(__rq));
 
 			if (elv_bio_merge_ok(__rq, bio)) {
-				ret = ELEVATOR_FRONT_MERGE;
-				goto out;
+				*req = __rq;
+				return ELEVATOR_FRONT_MERGE;
 			}
 		}
 	}
 
 	return ELEVATOR_NO_MERGE;
-out:
-	*req = __rq;
-	return ret;
 }
 
 static void deadline_merged_request(struct request_queue *q,
-				    struct request *req, int type)
+				    struct request *req, enum elv_merge type)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 
diff --git a/block/elevator.c b/block/elevator.c
index 7e4f5880dd64..27ff1ed5a6fa 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -427,11 +427,11 @@ void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 }
 EXPORT_SYMBOL(elv_dispatch_add_tail);
 
-int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
+enum elv_merge elv_merge(struct request_queue *q, struct request **req,
+		struct bio *bio)
 {
 	struct elevator_queue *e = q->elevator;
 	struct request *__rq;
-	int ret;
 
 	/*
 	 * Levels of merges:
@@ -446,7 +446,8 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 	 * First try one-hit cache.
 	 */
 	if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
-		ret = blk_try_merge(q->last_merge, bio);
+		enum elv_merge ret = blk_try_merge(q->last_merge, bio);
+
 		if (ret != ELEVATOR_NO_MERGE) {
 			*req = q->last_merge;
 			return ret;
@@ -514,7 +515,8 @@ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq)
 	return ret;
 }
 
-void elv_merged_request(struct request_queue *q, struct request *rq, int type)
+void elv_merged_request(struct request_queue *q, struct request *rq,
+		enum elv_merge type)
 {
 	struct elevator_queue *e = q->elevator;
 
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index d68d9c273a66..236121633ca0 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -121,7 +121,7 @@ static void deadline_remove_request(struct request_queue *q, struct request *rq)
 }
 
 static void dd_request_merged(struct request_queue *q, struct request *req,
-			      int type)
+			      enum elv_merge type)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index b5825c4f06f7..b38b4e651ea6 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -9,12 +9,21 @@
 struct io_cq;
 struct elevator_type;
 
-typedef int (elevator_merge_fn) (struct request_queue *, struct request **,
+/*
+ * Return values from elevator merger
+ */
+enum elv_merge {
+	ELEVATOR_NO_MERGE	= 0,
+	ELEVATOR_FRONT_MERGE	= 1,
+	ELEVATOR_BACK_MERGE	= 2,
+};
+
+typedef enum elv_merge (elevator_merge_fn) (struct request_queue *, struct request **,
 				 struct bio *);
 
 typedef void (elevator_merge_req_fn) (struct request_queue *, struct request *, struct request *);
 
-typedef void (elevator_merged_fn) (struct request_queue *, struct request *, int);
+typedef void (elevator_merged_fn) (struct request_queue *, struct request *, enum elv_merge);
 
 typedef int (elevator_allow_bio_merge_fn) (struct request_queue *,
 					   struct request *, struct bio *);
@@ -87,7 +96,7 @@ struct elevator_mq_ops {
 	bool (*allow_merge)(struct request_queue *, struct request *, struct bio *);
 	bool (*bio_merge)(struct blk_mq_hw_ctx *, struct bio *);
 	int (*request_merge)(struct request_queue *q, struct request **, struct bio *);
-	void (*request_merged)(struct request_queue *, struct request *, int);
+	void (*request_merged)(struct request_queue *, struct request *, enum elv_merge);
 	void (*requests_merged)(struct request_queue *, struct request *, struct request *);
 	struct request *(*get_request)(struct request_queue *, unsigned int, struct blk_mq_alloc_data *);
 	void (*put_request)(struct request *);
@@ -166,10 +175,12 @@ extern void elv_dispatch_sort(struct request_queue *, struct request *);
 extern void elv_dispatch_add_tail(struct request_queue *, struct request *);
 extern void elv_add_request(struct request_queue *, struct request *, int);
 extern void __elv_add_request(struct request_queue *, struct request *, int);
-extern int elv_merge(struct request_queue *, struct request **, struct bio *);
+extern enum elv_merge elv_merge(struct request_queue *, struct request **,
+		struct bio *);
 extern void elv_merge_requests(struct request_queue *, struct request *,
 			       struct request *);
-extern void elv_merged_request(struct request_queue *, struct request *, int);
+extern void elv_merged_request(struct request_queue *, struct request *,
+		enum elv_merge);
 extern void elv_bio_merged(struct request_queue *q, struct request *,
 				struct bio *);
 extern bool elv_attempt_insert_merge(struct request_queue *, struct request *);
@@ -219,13 +230,6 @@ extern void elv_rb_del(struct rb_root *, struct request *);
 extern struct request *elv_rb_find(struct rb_root *, sector_t);
 
 /*
- * Return values from elevator merger
- */
-#define ELEVATOR_NO_MERGE	0
-#define ELEVATOR_FRONT_MERGE	1
-#define ELEVATOR_BACK_MERGE	2
-
-/*
  * Insertion selection
  */
 #define ELEVATOR_INSERT_FRONT	1
-- 
2.11.0

[PATCH 2/4] block: enumify ELEVATOR_*_MERGE

[Christoph Hellwig]

Switch these constants to an enum, and make let the compiler ensure that
all callers of blk_try_merge and elv_merge handle all potential values.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-core.c         | 76 +++++++++++++++++++++++++-----------------------
 block/blk-merge.c        |  2 +-
 block/blk-mq-sched.c     | 35 +++++++++++-----------
 block/blk-mq.c           | 32 +++++++++-----------
 block/blk.h              |  2 +-
 block/cfq-iosched.c      |  4 +--
 block/deadline-iosched.c | 12 +++-----
 block/elevator.c         | 10 ++++---
 block/mq-deadline.c      |  2 +-
 include/linux/elevator.h | 28 ++++++++++--------
 10 files changed, 102 insertions(+), 101 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index d161d4ab7052..75fe534861df 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1513,12 +1513,11 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 {
 	struct blk_plug *plug;
 	struct request *rq;
-	bool ret = false;
 	struct list_head *plug_list;
 
 	plug = current->plug;
 	if (!plug)
-		goto out;
+		return false;
 	*request_count = 0;
 
 	if (q->mq_ops)
@@ -1527,7 +1526,7 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		plug_list = &plug->list;
 
 	list_for_each_entry_reverse(rq, plug_list, queuelist) {
-		int el_ret;
+		bool merged = false;
 
 		if (rq->q == q) {
 			(*request_count)++;
@@ -1543,19 +1542,22 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		if (rq->q != q || !blk_rq_merge_ok(rq, bio))
 			continue;
 
-		el_ret = blk_try_merge(rq, bio);
-		if (el_ret == ELEVATOR_BACK_MERGE) {
-			ret = bio_attempt_back_merge(q, rq, bio);
-			if (ret)
-				break;
-		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-			ret = bio_attempt_front_merge(q, rq, bio);
-			if (ret)
-				break;
+		switch (blk_try_merge(rq, bio)) {
+		case ELEVATOR_BACK_MERGE:
+			merged = bio_attempt_back_merge(q, rq, bio);
+			break;
+		case ELEVATOR_FRONT_MERGE:
+			merged = bio_attempt_front_merge(q, rq, bio);
+			break;
+		default:
+			break;
 		}
+
+		if (merged)
+			return true;
 	}
-out:
-	return ret;
+
+	return false;
 }
 
 unsigned int blk_plug_queued_count(struct request_queue *q)
@@ -1597,7 +1599,7 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 {
 	struct blk_plug *plug;
-	int el_ret, where = ELEVATOR_INSERT_SORT;
+	int where = ELEVATOR_INSERT_SORT;
 	struct request *req, *free;
 	unsigned int request_count = 0;
 	unsigned int wb_acct;
@@ -1635,27 +1637,29 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 
 	spin_lock_irq(q->queue_lock);
 
-	el_ret = elv_merge(q, &req, bio);
-	if (el_ret == ELEVATOR_BACK_MERGE) {
-		if (bio_attempt_back_merge(q, req, bio)) {
-			elv_bio_merged(q, req, bio);
-			free = attempt_back_merge(q, req);
-			if (!free)
-				elv_merged_request(q, req, el_ret);
-			else
-				__blk_put_request(q, free);
-			goto out_unlock;
-		}
-	} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-		if (bio_attempt_front_merge(q, req, bio)) {
-			elv_bio_merged(q, req, bio);
-			free = attempt_front_merge(q, req);
-			if (!free)
-				elv_merged_request(q, req, el_ret);
-			else
-				__blk_put_request(q, free);
-			goto out_unlock;
-		}
+	switch (elv_merge(q, &req, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		if (!bio_attempt_back_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_back_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_BACK_MERGE);
+		goto out_unlock;
+	case ELEVATOR_FRONT_MERGE:
+		if (!bio_attempt_front_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_front_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_FRONT_MERGE);
+		goto out_unlock;
+	default:
+		break;
 	}
 
 get_rq:
diff --git a/block/blk-merge.c b/block/blk-merge.c
index c956d9e7aafd..6cbd90ad5f90 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -801,7 +801,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 	return true;
 }
 
-int blk_try_merge(struct request *rq, struct bio *bio)
+enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 {
 	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 		return ELEVATOR_BACK_MERGE;
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ee455e7cf9d8..72d0d8361175 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -238,30 +238,29 @@ bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 			    struct request **merged_request)
 {
 	struct request *rq;
-	int ret;
 
-	ret = elv_merge(q, &rq, bio);
-	if (ret == ELEVATOR_BACK_MERGE) {
+	switch (elv_merge(q, &rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_back_merge(q, rq, bio)) {
-			*merged_request = attempt_back_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
-	} else if (ret == ELEVATOR_FRONT_MERGE) {
+		if (!bio_attempt_back_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_back_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
+		return true;
+	case ELEVATOR_FRONT_MERGE:
 		if (!blk_mq_sched_allow_merge(q, rq, bio))
 			return false;
-		if (bio_attempt_front_merge(q, rq, bio)) {
-			*merged_request = attempt_front_merge(q, rq);
-			if (!*merged_request)
-				elv_merged_request(q, rq, ret);
-			return true;
-		}
+		if (!bio_attempt_front_merge(q, rq, bio))
+			return false;
+		*merged_request = attempt_front_merge(q, rq);
+		if (!*merged_request)
+			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
+		return true;
+	default:
+		return false;
 	}
-
-	return false;
 }
 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index be183e6115a1..9294633759d9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -763,7 +763,7 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 	int checked = 8;
 
 	list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
-		int el_ret;
+		bool merged = false;
 
 		if (!checked--)
 			break;
@@ -771,26 +771,22 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 		if (!blk_rq_merge_ok(rq, bio))
 			continue;
 
-		el_ret = blk_try_merge(rq, bio);
-		if (el_ret == ELEVATOR_NO_MERGE)
-			continue;
-
-		if (!blk_mq_sched_allow_merge(q, rq, bio))
+		switch (blk_try_merge(rq, bio)) {
+		case ELEVATOR_BACK_MERGE:
+			if (blk_mq_sched_allow_merge(q, rq, bio))
+				merged = bio_attempt_back_merge(q, rq, bio);
 			break;
-
-		if (el_ret == ELEVATOR_BACK_MERGE) {
-			if (bio_attempt_back_merge(q, rq, bio)) {
-				ctx->rq_merged++;
-				return true;
-			}
-			break;
-		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
-			if (bio_attempt_front_merge(q, rq, bio)) {
-				ctx->rq_merged++;
-				return true;
-			}
+		case ELEVATOR_FRONT_MERGE:
+			if (blk_mq_sched_allow_merge(q, rq, bio))
+				merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		default:
+			continue;
 		}
+
+		if (merged)
+			ctx->rq_merged++;
+		return merged;
 	}
 
 	return false;
diff --git a/block/blk.h b/block/blk.h
index 3e08703902a9..ae82f2ac4019 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -215,7 +215,7 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 void blk_recalc_rq_segments(struct request *rq);
 void blk_rq_set_mixed_merge(struct request *rq);
 bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
-int blk_try_merge(struct request *rq, struct bio *bio);
+enum elv_merge blk_try_merge(struct request *rq, struct bio *bio);
 
 void blk_queue_congestion_threshold(struct request_queue *q);
 
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f0f29ee731e1..921262770636 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2528,7 +2528,7 @@ static void cfq_remove_request(struct request *rq)
 	}
 }
 
-static int cfq_merge(struct request_queue *q, struct request **req,
+static enum elv_merge cfq_merge(struct request_queue *q, struct request **req,
 		     struct bio *bio)
 {
 	struct cfq_data *cfqd = q->elevator->elevator_data;
@@ -2544,7 +2544,7 @@ static int cfq_merge(struct request_queue *q, struct request **req,
 }
 
 static void cfq_merged_request(struct request_queue *q, struct request *req,
-			       int type)
+			       enum elv_merge type)
 {
 	if (type == ELEVATOR_FRONT_MERGE) {
 		struct cfq_queue *cfqq = RQ_CFQQ(req);
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 05fc0ea25a98..c68f6bbc0dcd 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -120,12 +120,11 @@ static void deadline_remove_request(struct request_queue *q, struct request *rq)
 	deadline_del_rq_rb(dd, rq);
 }
 
-static int
+static enum elv_merge
 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 	struct request *__rq;
-	int ret;
 
 	/*
 	 * check for front merge
@@ -138,20 +137,17 @@ deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
 			BUG_ON(sector != blk_rq_pos(__rq));
 
 			if (elv_bio_merge_ok(__rq, bio)) {
-				ret = ELEVATOR_FRONT_MERGE;
-				goto out;
+				*req = __rq;
+				return ELEVATOR_FRONT_MERGE;
 			}
 		}
 	}
 
 	return ELEVATOR_NO_MERGE;
-out:
-	*req = __rq;
-	return ret;
 }
 
 static void deadline_merged_request(struct request_queue *q,
-				    struct request *req, int type)
+				    struct request *req, enum elv_merge type)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 
diff --git a/block/elevator.c b/block/elevator.c
index 7e4f5880dd64..27ff1ed5a6fa 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -427,11 +427,11 @@ void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
 }
 EXPORT_SYMBOL(elv_dispatch_add_tail);
 
-int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
+enum elv_merge elv_merge(struct request_queue *q, struct request **req,
+		struct bio *bio)
 {
 	struct elevator_queue *e = q->elevator;
 	struct request *__rq;
-	int ret;
 
 	/*
 	 * Levels of merges:
@@ -446,7 +446,8 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
 	 * First try one-hit cache.
 	 */
 	if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
-		ret = blk_try_merge(q->last_merge, bio);
+		enum elv_merge ret = blk_try_merge(q->last_merge, bio);
+
 		if (ret != ELEVATOR_NO_MERGE) {
 			*req = q->last_merge;
 			return ret;
@@ -514,7 +515,8 @@ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq)
 	return ret;
 }
 
-void elv_merged_request(struct request_queue *q, struct request *rq, int type)
+void elv_merged_request(struct request_queue *q, struct request *rq,
+		enum elv_merge type)
 {
 	struct elevator_queue *e = q->elevator;
 
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index d68d9c273a66..236121633ca0 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -121,7 +121,7 @@ static void deadline_remove_request(struct request_queue *q, struct request *rq)
 }
 
 static void dd_request_merged(struct request_queue *q, struct request *req,
-			      int type)
+			      enum elv_merge type)
 {
 	struct deadline_data *dd = q->elevator->elevator_data;
 
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index b5825c4f06f7..b38b4e651ea6 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -9,12 +9,21 @@
 struct io_cq;
 struct elevator_type;
 
-typedef int (elevator_merge_fn) (struct request_queue *, struct request **,
+/*
+ * Return values from elevator merger
+ */
+enum elv_merge {
+	ELEVATOR_NO_MERGE	= 0,
+	ELEVATOR_FRONT_MERGE	= 1,
+	ELEVATOR_BACK_MERGE	= 2,
+};
+
+typedef enum elv_merge (elevator_merge_fn) (struct request_queue *, struct request **,
 				 struct bio *);
 
 typedef void (elevator_merge_req_fn) (struct request_queue *, struct request *, struct request *);
 
-typedef void (elevator_merged_fn) (struct request_queue *, struct request *, int);
+typedef void (elevator_merged_fn) (struct request_queue *, struct request *, enum elv_merge);
 
 typedef int (elevator_allow_bio_merge_fn) (struct request_queue *,
 					   struct request *, struct bio *);
@@ -87,7 +96,7 @@ struct elevator_mq_ops {
 	bool (*allow_merge)(struct request_queue *, struct request *, struct bio *);
 	bool (*bio_merge)(struct blk_mq_hw_ctx *, struct bio *);
 	int (*request_merge)(struct request_queue *q, struct request **, struct bio *);
-	void (*request_merged)(struct request_queue *, struct request *, int);
+	void (*request_merged)(struct request_queue *, struct request *, enum elv_merge);
 	void (*requests_merged)(struct request_queue *, struct request *, struct request *);
 	struct request *(*get_request)(struct request_queue *, unsigned int, struct blk_mq_alloc_data *);
 	void (*put_request)(struct request *);
@@ -166,10 +175,12 @@ extern void elv_dispatch_sort(struct request_queue *, struct request *);
 extern void elv_dispatch_add_tail(struct request_queue *, struct request *);
 extern void elv_add_request(struct request_queue *, struct request *, int);
 extern void __elv_add_request(struct request_queue *, struct request *, int);
-extern int elv_merge(struct request_queue *, struct request **, struct bio *);
+extern enum elv_merge elv_merge(struct request_queue *, struct request **,
+		struct bio *);
 extern void elv_merge_requests(struct request_queue *, struct request *,
 			       struct request *);
-extern void elv_merged_request(struct request_queue *, struct request *, int);
+extern void elv_merged_request(struct request_queue *, struct request *,
+		enum elv_merge);
 extern void elv_bio_merged(struct request_queue *q, struct request *,
 				struct bio *);
 extern bool elv_attempt_insert_merge(struct request_queue *, struct request *);
@@ -219,13 +230,6 @@ extern void elv_rb_del(struct rb_root *, struct request *);
 extern struct request *elv_rb_find(struct rb_root *, sector_t);
 
 /*
- * Return values from elevator merger
- */
-#define ELEVATOR_NO_MERGE	0
-#define ELEVATOR_FRONT_MERGE	1
-#define ELEVATOR_BACK_MERGE	2
-
-/*
  * Insertion selection
  */
 #define ELEVATOR_INSERT_FRONT	1
-- 
2.11.0

[PATCH 3/4] block: optionally merge discontiguous discard bios into a single request

[Christoph Hellwig]

Add a new merge strategy that merges discard bios into a request until the
maximum number of discard ranges (or the maximum discard size) is reached
from the plug merging code.  I/O scheduler merging is not wired up yet
but might also be useful, although not for fast devices like NVMe which
are the only user for now.

Note that for now we don't support limiting the size of each discard range,
but if needed that can be added later.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-core.c         | 27 +++++++++++++++++++++++++++
 block/blk-merge.c        |  5 ++++-
 block/blk-mq.c           |  3 +++
 block/blk-settings.c     | 20 ++++++++++++++++++++
 block/blk-sysfs.c        | 12 ++++++++++++
 block/blk.h              |  2 ++
 include/linux/blkdev.h   | 26 ++++++++++++++++++++++++++
 include/linux/elevator.h |  1 +
 8 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 75fe534861df..b9e857f4afe8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1485,6 +1485,30 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
 	return true;
 }
 
+bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct bio *bio)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req);
+
+	if (segments >= queue_max_discard_segments(q))
+		goto no_merge;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		goto no_merge;
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+	req->nr_phys_segments = segments + 1;
+
+	blk_account_io_start(req, false);
+	return true;
+no_merge:
+	req_set_nomerge(q, req);
+	return false;
+}
+
 /**
  * blk_attempt_plug_merge - try to merge with %current's plugged list
  * @q: request_queue new bio is being queued at
@@ -1549,6 +1573,9 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		case ELEVATOR_FRONT_MERGE:
 			merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		case ELEVATOR_DISCARD_MERGE:
+			merged = bio_attempt_discard_merge(q, rq, bio);
+			break;
 		default:
 			break;
 		}
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 6cbd90ad5f90..2afa262425d1 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -803,7 +803,10 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 
 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 {
-	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
+	if (req_op(rq) == REQ_OP_DISCARD &&
+	    queue_max_discard_segments(rq->q) > 1)
+		return ELEVATOR_DISCARD_MERGE;
+	else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 		return ELEVATOR_BACK_MERGE;
 	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 		return ELEVATOR_FRONT_MERGE;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9294633759d9..89cb2d224488 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -780,6 +780,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 			if (blk_mq_sched_allow_merge(q, rq, bio))
 				merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		case ELEVATOR_DISCARD_MERGE:
+			merged = bio_attempt_discard_merge(q, rq, bio);
+			break;
 		default:
 			continue;
 		}
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 6eb19bcbf3cb..1e7174ffc9d4 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -88,6 +88,7 @@ EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
 void blk_set_default_limits(struct queue_limits *lim)
 {
 	lim->max_segments = BLK_MAX_SEGMENTS;
+	lim->max_discard_segments = 1;
 	lim->max_integrity_segments = 0;
 	lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
 	lim->virt_boundary_mask = 0;
@@ -128,6 +129,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 	/* Inherit limits from component devices */
 	lim->discard_zeroes_data = 1;
 	lim->max_segments = USHRT_MAX;
+	lim->max_discard_segments = 1;
 	lim->max_hw_sectors = UINT_MAX;
 	lim->max_segment_size = UINT_MAX;
 	lim->max_sectors = UINT_MAX;
@@ -337,6 +339,22 @@ void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments
 EXPORT_SYMBOL(blk_queue_max_segments);
 
 /**
+ * blk_queue_max_discard_segments - set max segments for discard requests
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    segments in a discard request.
+ **/
+void blk_queue_max_discard_segments(struct request_queue *q,
+		unsigned short max_segments)
+{
+	q->limits.max_discard_segments = max_segments;
+}
+EXPORT_SYMBOL_GPL(blk_queue_max_discard_segments);
+
+/**
  * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
  * @q:  the request queue for the device
  * @max_size:  max size of segment in bytes
@@ -553,6 +571,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 					    b->virt_boundary_mask);
 
 	t->max_segments = min_not_zero(t->max_segments, b->max_segments);
+	t->max_discard_segments = min_not_zero(t->max_discard_segments,
+					       b->max_discard_segments);
 	t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
 						 b->max_integrity_segments);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 48032c4759a7..070d81bae1d5 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -121,6 +121,12 @@ static ssize_t queue_max_segments_show(struct request_queue *q, char *page)
 	return queue_var_show(queue_max_segments(q), (page));
 }
 
+static ssize_t queue_max_discard_segments_show(struct request_queue *q,
+		char *page)
+{
+	return queue_var_show(queue_max_discard_segments(q), (page));
+}
+
 static ssize_t queue_max_integrity_segments_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(q->limits.max_integrity_segments, (page));
@@ -545,6 +551,11 @@ static struct queue_sysfs_entry queue_max_segments_entry = {
 	.show = queue_max_segments_show,
 };
 
+static struct queue_sysfs_entry queue_max_discard_segments_entry = {
+	.attr = {.name = "max_discard_segments", .mode = S_IRUGO },
+	.show = queue_max_discard_segments_show,
+};
+
 static struct queue_sysfs_entry queue_max_integrity_segments_entry = {
 	.attr = {.name = "max_integrity_segments", .mode = S_IRUGO },
 	.show = queue_max_integrity_segments_show,
@@ -697,6 +708,7 @@ static struct attribute *default_attrs[] = {
 	&queue_max_hw_sectors_entry.attr,
 	&queue_max_sectors_entry.attr,
 	&queue_max_segments_entry.attr,
+	&queue_max_discard_segments_entry.attr,
 	&queue_max_integrity_segments_entry.attr,
 	&queue_max_segment_size_entry.attr,
 	&queue_iosched_entry.attr,
diff --git a/block/blk.h b/block/blk.h
index ae82f2ac4019..d1ea4bd9b9a3 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -100,6 +100,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
 			     struct bio *bio);
 bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
 			    struct bio *bio);
+bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct bio *bio);
 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 			    unsigned int *request_count,
 			    struct request **same_queue_rq);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e0bac14347e6..aecca0e7d9ca 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -331,6 +331,7 @@ struct queue_limits {
 	unsigned short		logical_block_size;
 	unsigned short		max_segments;
 	unsigned short		max_integrity_segments;
+	unsigned short		max_discard_segments;
 
 	unsigned char		misaligned;
 	unsigned char		discard_misaligned;
@@ -1146,6 +1147,8 @@ extern void blk_queue_bounce_limit(struct request_queue *, u64);
 extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_max_segments(struct request_queue *, unsigned short);
+extern void blk_queue_max_discard_segments(struct request_queue *,
+		unsigned short);
 extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
 extern void blk_queue_max_discard_sectors(struct request_queue *q,
 		unsigned int max_discard_sectors);
@@ -1189,6 +1192,15 @@ extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
 extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
 
+/*
+ * Number of physical segments as sent to the device.
+ *
+ * Normally this is the number of discontiguous data segments sent by the
+ * submitter.  But for data-less command like discard we might have no
+ * actual data segments submitted, but the driver might have to add it's
+ * own special payload.  In that case we still return 1 here so that this
+ * special payload will be mapped.
+ */
 static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
 {
 	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
@@ -1196,6 +1208,15 @@ static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
 	return rq->nr_phys_segments;
 }
 
+/*
+ * Number of discard segments (or ranges) the driver needs to fill in.
+ * Each discard bio merged into a request is counted as one segment.
+ */
+static inline unsigned short blk_rq_nr_discard_segments(struct request *rq)
+{
+	return max_t(unsigned short, rq->nr_phys_segments, 1);
+}
+
 extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
 extern void blk_dump_rq_flags(struct request *, char *);
 extern long nr_blockdev_pages(void);
@@ -1384,6 +1405,11 @@ static inline unsigned short queue_max_segments(struct request_queue *q)
 	return q->limits.max_segments;
 }
 
+static inline unsigned short queue_max_discard_segments(struct request_queue *q)
+{
+	return q->limits.max_discard_segments;
+}
+
 static inline unsigned int queue_max_segment_size(struct request_queue *q)
 {
 	return q->limits.max_segment_size;
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index b38b4e651ea6..8265b6330cc2 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -16,6 +16,7 @@ enum elv_merge {
 	ELEVATOR_NO_MERGE	= 0,
 	ELEVATOR_FRONT_MERGE	= 1,
 	ELEVATOR_BACK_MERGE	= 2,
+	ELEVATOR_DISCARD_MERGE	= 3,
 };
 
 typedef enum elv_merge (elevator_merge_fn) (struct request_queue *, struct request **,
-- 
2.11.0

[PATCH 3/4] block: optionally merge discontiguous discard bios into a single request

[Christoph Hellwig]

Add a new merge strategy that merges discard bios into a request until the
maximum number of discard ranges (or the maximum discard size) is reached
from the plug merging code.  I/O scheduler merging is not wired up yet
but might also be useful, although not for fast devices like NVMe which
are the only user for now.

Note that for now we don't support limiting the size of each discard range,
but if needed that can be added later.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-core.c         | 27 +++++++++++++++++++++++++++
 block/blk-merge.c        |  5 ++++-
 block/blk-mq.c           |  3 +++
 block/blk-settings.c     | 20 ++++++++++++++++++++
 block/blk-sysfs.c        | 12 ++++++++++++
 block/blk.h              |  2 ++
 include/linux/blkdev.h   | 26 ++++++++++++++++++++++++++
 include/linux/elevator.h |  1 +
 8 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 75fe534861df..b9e857f4afe8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1485,6 +1485,30 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
 	return true;
 }
 
+bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct bio *bio)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req);
+
+	if (segments >= queue_max_discard_segments(q))
+		goto no_merge;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		goto no_merge;
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+	req->nr_phys_segments = segments + 1;
+
+	blk_account_io_start(req, false);
+	return true;
+no_merge:
+	req_set_nomerge(q, req);
+	return false;
+}
+
 /**
  * blk_attempt_plug_merge - try to merge with %current's plugged list
  * @q: request_queue new bio is being queued at
@@ -1549,6 +1573,9 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		case ELEVATOR_FRONT_MERGE:
 			merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		case ELEVATOR_DISCARD_MERGE:
+			merged = bio_attempt_discard_merge(q, rq, bio);
+			break;
 		default:
 			break;
 		}
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 6cbd90ad5f90..2afa262425d1 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -803,7 +803,10 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
 
 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
 {
-	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
+	if (req_op(rq) == REQ_OP_DISCARD &&
+	    queue_max_discard_segments(rq->q) > 1)
+		return ELEVATOR_DISCARD_MERGE;
+	else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
 		return ELEVATOR_BACK_MERGE;
 	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
 		return ELEVATOR_FRONT_MERGE;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9294633759d9..89cb2d224488 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -780,6 +780,9 @@ static bool blk_mq_attempt_merge(struct request_queue *q,
 			if (blk_mq_sched_allow_merge(q, rq, bio))
 				merged = bio_attempt_front_merge(q, rq, bio);
 			break;
+		case ELEVATOR_DISCARD_MERGE:
+			merged = bio_attempt_discard_merge(q, rq, bio);
+			break;
 		default:
 			continue;
 		}
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 6eb19bcbf3cb..1e7174ffc9d4 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -88,6 +88,7 @@ EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
 void blk_set_default_limits(struct queue_limits *lim)
 {
 	lim->max_segments = BLK_MAX_SEGMENTS;
+	lim->max_discard_segments = 1;
 	lim->max_integrity_segments = 0;
 	lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
 	lim->virt_boundary_mask = 0;
@@ -128,6 +129,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 	/* Inherit limits from component devices */
 	lim->discard_zeroes_data = 1;
 	lim->max_segments = USHRT_MAX;
+	lim->max_discard_segments = 1;
 	lim->max_hw_sectors = UINT_MAX;
 	lim->max_segment_size = UINT_MAX;
 	lim->max_sectors = UINT_MAX;
@@ -337,6 +339,22 @@ void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments
 EXPORT_SYMBOL(blk_queue_max_segments);
 
 /**
+ * blk_queue_max_discard_segments - set max segments for discard requests
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    segments in a discard request.
+ **/
+void blk_queue_max_discard_segments(struct request_queue *q,
+		unsigned short max_segments)
+{
+	q->limits.max_discard_segments = max_segments;
+}
+EXPORT_SYMBOL_GPL(blk_queue_max_discard_segments);
+
+/**
  * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
  * @q:  the request queue for the device
  * @max_size:  max size of segment in bytes
@@ -553,6 +571,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 					    b->virt_boundary_mask);
 
 	t->max_segments = min_not_zero(t->max_segments, b->max_segments);
+	t->max_discard_segments = min_not_zero(t->max_discard_segments,
+					       b->max_discard_segments);
 	t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
 						 b->max_integrity_segments);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 48032c4759a7..070d81bae1d5 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -121,6 +121,12 @@ static ssize_t queue_max_segments_show(struct request_queue *q, char *page)
 	return queue_var_show(queue_max_segments(q), (page));
 }
 
+static ssize_t queue_max_discard_segments_show(struct request_queue *q,
+		char *page)
+{
+	return queue_var_show(queue_max_discard_segments(q), (page));
+}
+
 static ssize_t queue_max_integrity_segments_show(struct request_queue *q, char *page)
 {
 	return queue_var_show(q->limits.max_integrity_segments, (page));
@@ -545,6 +551,11 @@ static struct queue_sysfs_entry queue_max_segments_entry = {
 	.show = queue_max_segments_show,
 };
 
+static struct queue_sysfs_entry queue_max_discard_segments_entry = {
+	.attr = {.name = "max_discard_segments", .mode = S_IRUGO },
+	.show = queue_max_discard_segments_show,
+};
+
 static struct queue_sysfs_entry queue_max_integrity_segments_entry = {
 	.attr = {.name = "max_integrity_segments", .mode = S_IRUGO },
 	.show = queue_max_integrity_segments_show,
@@ -697,6 +708,7 @@ static struct attribute *default_attrs[] = {
 	&queue_max_hw_sectors_entry.attr,
 	&queue_max_sectors_entry.attr,
 	&queue_max_segments_entry.attr,
+	&queue_max_discard_segments_entry.attr,
 	&queue_max_integrity_segments_entry.attr,
 	&queue_max_segment_size_entry.attr,
 	&queue_iosched_entry.attr,
diff --git a/block/blk.h b/block/blk.h
index ae82f2ac4019..d1ea4bd9b9a3 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -100,6 +100,8 @@ bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
 			     struct bio *bio);
 bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
 			    struct bio *bio);
+bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct bio *bio);
 bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 			    unsigned int *request_count,
 			    struct request **same_queue_rq);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e0bac14347e6..aecca0e7d9ca 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -331,6 +331,7 @@ struct queue_limits {
 	unsigned short		logical_block_size;
 	unsigned short		max_segments;
 	unsigned short		max_integrity_segments;
+	unsigned short		max_discard_segments;
 
 	unsigned char		misaligned;
 	unsigned char		discard_misaligned;
@@ -1146,6 +1147,8 @@ extern void blk_queue_bounce_limit(struct request_queue *, u64);
 extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
 extern void blk_queue_max_segments(struct request_queue *, unsigned short);
+extern void blk_queue_max_discard_segments(struct request_queue *,
+		unsigned short);
 extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
 extern void blk_queue_max_discard_sectors(struct request_queue *q,
 		unsigned int max_discard_sectors);
@@ -1189,6 +1192,15 @@ extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
 extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
 
+/*
+ * Number of physical segments as sent to the device.
+ *
+ * Normally this is the number of discontiguous data segments sent by the
+ * submitter.  But for data-less command like discard we might have no
+ * actual data segments submitted, but the driver might have to add it's
+ * own special payload.  In that case we still return 1 here so that this
+ * special payload will be mapped.
+ */
 static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
 {
 	if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
@@ -1196,6 +1208,15 @@ static inline unsigned short blk_rq_nr_phys_segments(struct request *rq)
 	return rq->nr_phys_segments;
 }
 
+/*
+ * Number of discard segments (or ranges) the driver needs to fill in.
+ * Each discard bio merged into a request is counted as one segment.
+ */
+static inline unsigned short blk_rq_nr_discard_segments(struct request *rq)
+{
+	return max_t(unsigned short, rq->nr_phys_segments, 1);
+}
+
 extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
 extern void blk_dump_rq_flags(struct request *, char *);
 extern long nr_blockdev_pages(void);
@@ -1384,6 +1405,11 @@ static inline unsigned short queue_max_segments(struct request_queue *q)
 	return q->limits.max_segments;
 }
 
+static inline unsigned short queue_max_discard_segments(struct request_queue *q)
+{
+	return q->limits.max_discard_segments;
+}
+
 static inline unsigned int queue_max_segment_size(struct request_queue *q)
 {
 	return q->limits.max_segment_size;
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index b38b4e651ea6..8265b6330cc2 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -16,6 +16,7 @@ enum elv_merge {
 	ELEVATOR_NO_MERGE	= 0,
 	ELEVATOR_FRONT_MERGE	= 1,
 	ELEVATOR_BACK_MERGE	= 2,
+	ELEVATOR_DISCARD_MERGE	= 3,
 };
 
 typedef enum elv_merge (elevator_merge_fn) (struct request_queue *, struct request **,
-- 
2.11.0

[PATCH 4/4] nvme: support ranged discard requests

[Christoph Hellwig]

NVMe supports up to 256 ranges per DSM command, so wire up support
for ranged discards up to that limit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/core.c | 30 +++++++++++++++++++++++-------
 include/linux/nvme.h     |  2 ++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index efe8ec300126..d9f49036819c 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -238,26 +238,38 @@ static inline void nvme_setup_flush(struct nvme_ns *ns,
 static inline int nvme_setup_discard(struct nvme_ns *ns, struct request *req,
 		struct nvme_command *cmnd)
 {
+	unsigned short segments = blk_rq_nr_discard_segments(req), n = 0;
 	struct nvme_dsm_range *range;
-	unsigned int nr_bytes = blk_rq_bytes(req);
+	struct bio *bio;
 
-	range = kmalloc(sizeof(*range), GFP_ATOMIC);
+	range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
 	if (!range)
 		return BLK_MQ_RQ_QUEUE_BUSY;
 
-	range->cattr = cpu_to_le32(0);
-	range->nlb = cpu_to_le32(nr_bytes >> ns->lba_shift);
-	range->slba = cpu_to_le64(nvme_block_nr(ns, blk_rq_pos(req)));
+	__rq_for_each_bio(bio, req) {
+		u64 slba = nvme_block_nr(ns, bio->bi_iter.bi_sector);
+		u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
+
+		range[n].cattr = cpu_to_le32(0);
+		range[n].nlb = cpu_to_le32(nlb);
+		range[n].slba = cpu_to_le64(slba);
+		n++;
+	}
+
+	if (WARN_ON_ONCE(n != segments)) {
+		kfree(range);
+		return BLK_MQ_RQ_QUEUE_ERROR;
+	}
 
 	memset(cmnd, 0, sizeof(*cmnd));
 	cmnd->dsm.opcode = nvme_cmd_dsm;
 	cmnd->dsm.nsid = cpu_to_le32(ns->ns_id);
-	cmnd->dsm.nr = 0;
+	cmnd->dsm.nr = segments - 1;
 	cmnd->dsm.attributes = cpu_to_le32(NVME_DSMGMT_AD);
 
 	req->special_vec.bv_page = virt_to_page(range);
 	req->special_vec.bv_offset = offset_in_page(range);
-	req->special_vec.bv_len = sizeof(*range);
+	req->special_vec.bv_len = sizeof(*range) * segments;
 	req->rq_flags |= RQF_SPECIAL_PAYLOAD;
 
 	return BLK_MQ_RQ_QUEUE_OK;
@@ -877,6 +889,9 @@ static void nvme_config_discard(struct nvme_ns *ns)
 	struct nvme_ctrl *ctrl = ns->ctrl;
 	u32 logical_block_size = queue_logical_block_size(ns->queue);
 
+	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct nvme_dsm_range) <
+			NVME_DSM_MAX_RANGES);
+
 	if (ctrl->quirks & NVME_QUIRK_DISCARD_ZEROES)
 		ns->queue->limits.discard_zeroes_data = 1;
 	else
@@ -885,6 +900,7 @@ static void nvme_config_discard(struct nvme_ns *ns)
 	ns->queue->limits.discard_alignment = logical_block_size;
 	ns->queue->limits.discard_granularity = logical_block_size;
 	blk_queue_max_discard_sectors(ns->queue, UINT_MAX);
+	blk_queue_max_discard_segments(ns->queue, NVME_DSM_MAX_RANGES);
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, ns->queue);
 }
 
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 3d1c6f1b15c9..3e2ed49c3ad8 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -553,6 +553,8 @@ enum {
 	NVME_DSMGMT_AD		= 1 << 2,
 };
 
+#define NVME_DSM_MAX_RANGES	256
+
 struct nvme_dsm_range {
 	__le32			cattr;
 	__le32			nlb;
-- 
2.11.0

[PATCH 4/4] nvme: support ranged discard requests

[Christoph Hellwig]

NVMe supports up to 256 ranges per DSM command, so wire up support
for ranged discards up to that limit.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/nvme/host/core.c | 30 +++++++++++++++++++++++-------
 include/linux/nvme.h     |  2 ++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index efe8ec300126..d9f49036819c 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -238,26 +238,38 @@ static inline void nvme_setup_flush(struct nvme_ns *ns,
 static inline int nvme_setup_discard(struct nvme_ns *ns, struct request *req,
 		struct nvme_command *cmnd)
 {
+	unsigned short segments = blk_rq_nr_discard_segments(req), n = 0;
 	struct nvme_dsm_range *range;
-	unsigned int nr_bytes = blk_rq_bytes(req);
+	struct bio *bio;
 
-	range = kmalloc(sizeof(*range), GFP_ATOMIC);
+	range = kmalloc_array(segments, sizeof(*range), GFP_ATOMIC);
 	if (!range)
 		return BLK_MQ_RQ_QUEUE_BUSY;
 
-	range->cattr = cpu_to_le32(0);
-	range->nlb = cpu_to_le32(nr_bytes >> ns->lba_shift);
-	range->slba = cpu_to_le64(nvme_block_nr(ns, blk_rq_pos(req)));
+	__rq_for_each_bio(bio, req) {
+		u64 slba = nvme_block_nr(ns, bio->bi_iter.bi_sector);
+		u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
+
+		range[n].cattr = cpu_to_le32(0);
+		range[n].nlb = cpu_to_le32(nlb);
+		range[n].slba = cpu_to_le64(slba);
+		n++;
+	}
+
+	if (WARN_ON_ONCE(n != segments)) {
+		kfree(range);
+		return BLK_MQ_RQ_QUEUE_ERROR;
+	}
 
 	memset(cmnd, 0, sizeof(*cmnd));
 	cmnd->dsm.opcode = nvme_cmd_dsm;
 	cmnd->dsm.nsid = cpu_to_le32(ns->ns_id);
-	cmnd->dsm.nr = 0;
+	cmnd->dsm.nr = segments - 1;
 	cmnd->dsm.attributes = cpu_to_le32(NVME_DSMGMT_AD);
 
 	req->special_vec.bv_page = virt_to_page(range);
 	req->special_vec.bv_offset = offset_in_page(range);
-	req->special_vec.bv_len = sizeof(*range);
+	req->special_vec.bv_len = sizeof(*range) * segments;
 	req->rq_flags |= RQF_SPECIAL_PAYLOAD;
 
 	return BLK_MQ_RQ_QUEUE_OK;
@@ -877,6 +889,9 @@ static void nvme_config_discard(struct nvme_ns *ns)
 	struct nvme_ctrl *ctrl = ns->ctrl;
 	u32 logical_block_size = queue_logical_block_size(ns->queue);
 
+	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct nvme_dsm_range) <
+			NVME_DSM_MAX_RANGES);
+
 	if (ctrl->quirks & NVME_QUIRK_DISCARD_ZEROES)
 		ns->queue->limits.discard_zeroes_data = 1;
 	else
@@ -885,6 +900,7 @@ static void nvme_config_discard(struct nvme_ns *ns)
 	ns->queue->limits.discard_alignment = logical_block_size;
 	ns->queue->limits.discard_granularity = logical_block_size;
 	blk_queue_max_discard_sectors(ns->queue, UINT_MAX);
+	blk_queue_max_discard_segments(ns->queue, NVME_DSM_MAX_RANGES);
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, ns->queue);
 }
 
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 3d1c6f1b15c9..3e2ed49c3ad8 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -553,6 +553,8 @@ enum {
 	NVME_DSMGMT_AD		= 1 << 2,
 };
 
+#define NVME_DSM_MAX_RANGES	256
+
 struct nvme_dsm_range {
 	__le32			cattr;
 	__le32			nlb;
-- 
2.11.0

Re: support for multi-range discard requests V3

[Jens Axboe]

On 02/08/2017 06:46 AM, Christoph Hellwig wrote:
> Hi all,
> 
> this series adds support for merging discontiguous discard bios into a
> single request if the driver supports it.  This reduces the number of
> discards sent to the device by about a factor of 5-6 for typical
> workloads on NVMe, and for slower devices that use I/O scheduling
> the number will probably be even bigger but I've not implemented
> that support yet.

This looks good to me. It's running testing now, but provided that
the tests are successful, we should get this queued up for 4.11.


-- 
Jens Axboe

support for multi-range discard requests V3

[Jens Axboe]

On 02/08/2017 06:46 AM, Christoph Hellwig wrote:
> Hi all,
> 
> this series adds support for merging discontiguous discard bios into a
> single request if the driver supports it.  This reduces the number of
> discards sent to the device by about a factor of 5-6 for typical
> workloads on NVMe, and for slower devices that use I/O scheduling
> the number will probably be even bigger but I've not implemented
> that support yet.

This looks good to me. It's running testing now, but provided that
the tests are successful, we should get this queued up for 4.11.


-- 
Jens Axboe

Re: support for multi-range discard requests V3

[Sagi Grimberg]

> Hi all,
>
> this series adds support for merging discontiguous discard bios into a
> single request if the driver supports it.  This reduces the number of
> discards sent to the device by about a factor of 5-6 for typical
> workloads on NVMe, and for slower devices that use I/O scheduling
> the number will probably be even bigger but I've not implemented
> that support yet.
>
> Changes since V2:
>   - really fix nr of NVMe ranges to 256
>   - free range on error
>
> Changes since V1:
>   - hardcoded max ranges for NVMe to 255
>   - minor cleanups

Oops, reviewed v1 before noticing this one...

support for multi-range discard requests V3

[Sagi Grimberg]

> Hi all,
>
> this series adds support for merging discontiguous discard bios into a
> single request if the driver supports it.  This reduces the number of
> discards sent to the device by about a factor of 5-6 for typical
> workloads on NVMe, and for slower devices that use I/O scheduling
> the number will probably be even bigger but I've not implemented
> that support yet.
>
> Changes since V2:
>   - really fix nr of NVMe ranges to 256
>   - free range on error
>
> Changes since V1:
>   - hardcoded max ranges for NVMe to 255
>   - minor cleanups

Oops, reviewed v1 before noticing this one...

Re: [PATCH 4/4] nvme: support ranged discard requests

[Sagi Grimberg]

Looks good,

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

[PATCH 4/4] nvme: support ranged discard requests

[Sagi Grimberg]

Looks good,

Reviewed-by: Sagi Grimberg <sagi at grimberg.me>