[PATCHv3 2/4] block: move elevator tags into struct elevator_resources

[Nilay Shroff <nilay@linux.ibm.com>]

This patch introduces a new structure, struct elevator_resources, to
group together all elevator-related resources that share the same
lifetime. As a first step, this change moves the elevator tag pointer
from struct elv_change_ctx into the new struct elevator_resources.

Additionally, rename blk_mq_alloc_sched_tags_batch() and
blk_mq_free_sched_tags_batch() to blk_mq_alloc_sched_res_batch() and
blk_mq_free_sched_res_batch(), respectively. Introduce two new wrapper
helpers, blk_mq_alloc_sched_res() and blk_mq_free_sched_res(), around
blk_mq_alloc_sched_tags() and blk_mq_free_sched_tags().

These changes pave the way for consolidating the allocation and freeing
of elevator-specific resources into common helper functions. This
refactoring improves encapsulation and prepares the code for future
extensions, allowing additional elevator-specific data to be added to
struct elevator_resources without cluttering struct elv_change_ctx.

Subsequent patches will extend struct elevator_resources to include
other elevator-related data.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 block/blk-mq-sched.c | 55 ++++++++++++++++++++++++++++----------------
 block/blk-mq-sched.h | 10 +++++---
 block/blk-mq.c       |  2 +-
 block/elevator.c     | 35 ++++++++++++++--------------
 block/elevator.h     | 11 ++++++---
 5 files changed, 69 insertions(+), 44 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 3d9386555a50..6db45b0819e6 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -427,7 +427,16 @@ void blk_mq_free_sched_tags(struct elevator_tags *et,
 	kfree(et);
 }
 
-void blk_mq_free_sched_tags_batch(struct xarray *elv_tbl,
+void blk_mq_free_sched_res(struct elevator_resources *res,
+		struct blk_mq_tag_set *set)
+{
+	if (res->et) {
+		blk_mq_free_sched_tags(res->et, set);
+		res->et = NULL;
+	}
+}
+
+void blk_mq_free_sched_res_batch(struct xarray *elv_tbl,
 		struct blk_mq_tag_set *set)
 {
 	struct request_queue *q;
@@ -445,12 +454,11 @@ void blk_mq_free_sched_tags_batch(struct xarray *elv_tbl,
 		 */
 		if (q->elevator) {
 			ctx = xa_load(elv_tbl, q->id);
-			if (!ctx || !ctx->et) {
+			if (!ctx) {
 				WARN_ON_ONCE(1);
 				continue;
 			}
-			blk_mq_free_sched_tags(ctx->et, set);
-			ctx->et = NULL;
+			blk_mq_free_sched_res(&ctx->res, set);
 		}
 	}
 }
@@ -532,12 +540,22 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 	return NULL;
 }
 
-int blk_mq_alloc_sched_tags_batch(struct xarray *elv_tbl,
+int blk_mq_alloc_sched_res(struct elevator_resources *res,
+		struct blk_mq_tag_set *set, unsigned int nr_hw_queues)
+{
+	res->et = blk_mq_alloc_sched_tags(set, nr_hw_queues,
+			blk_mq_default_nr_requests(set));
+	if (!res->et)
+		return -ENOMEM;
+
+	return 0;
+}
+
+int blk_mq_alloc_sched_res_batch(struct xarray *elv_tbl,
 		struct blk_mq_tag_set *set, unsigned int nr_hw_queues)
 {
 	struct elv_change_ctx *ctx;
 	struct request_queue *q;
-	struct elevator_tags *et;
 	int ret = -ENOMEM;
 
 	lockdep_assert_held_write(&set->update_nr_hwq_lock);
@@ -557,11 +575,10 @@ int blk_mq_alloc_sched_tags_batch(struct xarray *elv_tbl,
 				goto out_unwind;
 			}
 
-			ctx->et = blk_mq_alloc_sched_tags(set, nr_hw_queues,
-					blk_mq_default_nr_requests(set));
-			if (!ctx->et)
+			ret = blk_mq_alloc_sched_res(&ctx->res, set,
+					nr_hw_queues);
+			if (ret)
 				goto out_unwind;
-
 		}
 	}
 	return 0;
@@ -569,10 +586,8 @@ int blk_mq_alloc_sched_tags_batch(struct xarray *elv_tbl,
 	list_for_each_entry_continue_reverse(q, &set->tag_list, tag_set_list) {
 		if (q->elevator) {
 			ctx = xa_load(elv_tbl, q->id);
-			if (ctx && ctx->et) {
-				blk_mq_free_sched_tags(ctx->et, set);
-				ctx->et = NULL;
-			}
+			if (ctx)
+				blk_mq_free_sched_res(&ctx->res, set);
 		}
 	}
 	return ret;
@@ -580,7 +595,7 @@ int blk_mq_alloc_sched_tags_batch(struct xarray *elv_tbl,
 
 /* caller must have a reference to @e, will grab another one if successful */
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e,
-		struct elevator_tags *et)
+		struct elevator_resources *res)
 {
 	unsigned int flags = q->tag_set->flags;
 	struct blk_mq_hw_ctx *hctx;
@@ -588,23 +603,23 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e,
 	unsigned long i;
 	int ret;
 
-	eq = elevator_alloc(q, e, et);
+	eq = elevator_alloc(q, e, res);
 	if (!eq)
 		return -ENOMEM;
 
-	q->nr_requests = et->nr_requests;
+	q->nr_requests = res->et->nr_requests;
 
 	if (blk_mq_is_shared_tags(flags)) {
 		/* Shared tags are stored at index 0 in @et->tags. */
-		q->sched_shared_tags = et->tags[0];
-		blk_mq_tag_update_sched_shared_tags(q, et->nr_requests);
+		q->sched_shared_tags = res->et->tags[0];
+		blk_mq_tag_update_sched_shared_tags(q, res->et->nr_requests);
 	}
 
 	queue_for_each_hw_ctx(q, hctx, i) {
 		if (blk_mq_is_shared_tags(flags))
 			hctx->sched_tags = q->sched_shared_tags;
 		else
-			hctx->sched_tags = et->tags[i];
+			hctx->sched_tags = res->et->tags[i];
 	}
 
 	ret = e->ops.init_sched(q, eq);
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 2fddbc91a235..97204df76def 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -19,20 +19,24 @@ void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx);
 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
 
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e,
-		struct elevator_tags *et);
+		struct elevator_resources *res);
 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
 void blk_mq_sched_free_rqs(struct request_queue *q);
 
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 		unsigned int nr_hw_queues, unsigned int nr_requests);
-int blk_mq_alloc_sched_tags_batch(struct xarray *et_table,
+int blk_mq_alloc_sched_res(struct elevator_resources *res,
+		struct blk_mq_tag_set *set, unsigned int nr_hw_queues);
+int blk_mq_alloc_sched_res_batch(struct xarray *elv_tbl,
 		struct blk_mq_tag_set *set, unsigned int nr_hw_queues);
 int blk_mq_alloc_sched_ctx_batch(struct xarray *elv_tbl,
 		struct blk_mq_tag_set *set);
 void blk_mq_free_sched_ctx_batch(struct xarray *elv_tbl);
 void blk_mq_free_sched_tags(struct elevator_tags *et,
 		struct blk_mq_tag_set *set);
-void blk_mq_free_sched_tags_batch(struct xarray *et_table,
+void blk_mq_free_sched_res(struct elevator_resources *res,
+		struct blk_mq_tag_set *set);
+void blk_mq_free_sched_res_batch(struct xarray *et_table,
 		struct blk_mq_tag_set *set);
 
 static inline void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1f5ef7fc9cda..2535271875bb 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -5066,7 +5066,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 	if (blk_mq_alloc_sched_ctx_batch(&elv_tbl, set) < 0)
 		goto out_free_ctx;
 
-	if (blk_mq_alloc_sched_tags_batch(&elv_tbl, set, nr_hw_queues) < 0)
+	if (blk_mq_alloc_sched_res_batch(&elv_tbl, set, nr_hw_queues) < 0)
 		goto out_free_ctx;
 
 	list_for_each_entry(q, &set->tag_list, tag_set_list) {
diff --git a/block/elevator.c b/block/elevator.c
index cd7bdff205c8..d5d89b202fda 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -121,7 +121,7 @@ static struct elevator_type *elevator_find_get(const char *name)
 static const struct kobj_type elv_ktype;
 
 struct elevator_queue *elevator_alloc(struct request_queue *q,
-		struct elevator_type *e, struct elevator_tags *et)
+		struct elevator_type *e, struct elevator_resources *res)
 {
 	struct elevator_queue *eq;
 
@@ -134,7 +134,7 @@ struct elevator_queue *elevator_alloc(struct request_queue *q,
 	kobject_init(&eq->kobj, &elv_ktype);
 	mutex_init(&eq->sysfs_lock);
 	hash_init(eq->hash);
-	eq->et = et;
+	eq->et = res->et;
 
 	return eq;
 }
@@ -580,7 +580,7 @@ static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
 	}
 
 	if (new_e) {
-		ret = blk_mq_init_sched(q, new_e, ctx->et);
+		ret = blk_mq_init_sched(q, new_e, &ctx->res);
 		if (ret)
 			goto out_unfreeze;
 		ctx->new = q->elevator;
@@ -604,7 +604,8 @@ static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
 	return ret;
 }
 
-static void elv_exit_and_release(struct request_queue *q)
+static void elv_exit_and_release(struct elv_change_ctx *ctx,
+		struct request_queue *q)
 {
 	struct elevator_queue *e;
 	unsigned memflags;
@@ -616,7 +617,7 @@ static void elv_exit_and_release(struct request_queue *q)
 	mutex_unlock(&q->elevator_lock);
 	blk_mq_unfreeze_queue(q, memflags);
 	if (e) {
-		blk_mq_free_sched_tags(e->et, q->tag_set);
+		blk_mq_free_sched_res(&ctx->res, q->tag_set);
 		kobject_put(&e->kobj);
 	}
 }
@@ -627,11 +628,12 @@ static int elevator_change_done(struct request_queue *q,
 	int ret = 0;
 
 	if (ctx->old) {
+		struct elevator_resources res = {.et = ctx->old->et};
 		bool enable_wbt = test_bit(ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT,
 				&ctx->old->flags);
 
 		elv_unregister_queue(q, ctx->old);
-		blk_mq_free_sched_tags(ctx->old->et, q->tag_set);
+		blk_mq_free_sched_res(&res, q->tag_set);
 		kobject_put(&ctx->old->kobj);
 		if (enable_wbt)
 			wbt_enable_default(q->disk);
@@ -639,7 +641,7 @@ static int elevator_change_done(struct request_queue *q,
 	if (ctx->new) {
 		ret = elv_register_queue(q, ctx->new, !ctx->no_uevent);
 		if (ret)
-			elv_exit_and_release(q);
+			elv_exit_and_release(ctx, q);
 	}
 	return ret;
 }
@@ -656,10 +658,9 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	lockdep_assert_held(&set->update_nr_hwq_lock);
 
 	if (strncmp(ctx->name, "none", 4)) {
-		ctx->et = blk_mq_alloc_sched_tags(set, set->nr_hw_queues,
-				blk_mq_default_nr_requests(set));
-		if (!ctx->et)
-			return -ENOMEM;
+		ret = blk_mq_alloc_sched_res(&ctx->res, set, set->nr_hw_queues);
+		if (ret)
+			return ret;
 	}
 
 	memflags = blk_mq_freeze_queue(q);
@@ -681,10 +682,10 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	if (!ret)
 		ret = elevator_change_done(q, ctx);
 	/*
-	 * Free sched tags if it's allocated but we couldn't switch elevator.
+	 * Free sched resource if it's allocated but we couldn't switch elevator.
 	 */
-	if (ctx->et && !ctx->new)
-		blk_mq_free_sched_tags(ctx->et, set);
+	if (!ctx->new)
+		blk_mq_free_sched_res(&ctx->res, set);
 
 	return ret;
 }
@@ -711,10 +712,10 @@ void elv_update_nr_hw_queues(struct request_queue *q,
 	if (!ret)
 		WARN_ON_ONCE(elevator_change_done(q, ctx));
 	/*
-	 * Free sched tags if it's allocated but we couldn't switch elevator.
+	 * Free sched resource if it's allocated but we couldn't switch elevator.
 	 */
-	if (ctx->et && !ctx->new)
-		blk_mq_free_sched_tags(ctx->et, set);
+	if (!ctx->new)
+		blk_mq_free_sched_res(&ctx->res, set);
 }
 
 /*
diff --git a/block/elevator.h b/block/elevator.h
index bad43182361e..6533f74ad5ef 100644
--- a/block/elevator.h
+++ b/block/elevator.h
@@ -32,6 +32,11 @@ struct elevator_tags {
 	struct blk_mq_tags *tags[];
 };
 
+struct elevator_resources {
+	/* holds elevator tags */
+	struct elevator_tags *et;
+};
+
 /* Holding context data for changing elevator */
 struct elv_change_ctx {
 	const char *name;
@@ -43,8 +48,8 @@ struct elv_change_ctx {
 	struct elevator_queue *new;
 	/* store elevator type */
 	struct elevator_type *type;
-	/* holds sched tags data */
-	struct elevator_tags *et;
+	/* store elevator resources */
+	struct elevator_resources res;
 };
 
 struct elevator_mq_ops {
@@ -178,7 +183,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *page, size_t count);
 
 extern bool elv_bio_merge_ok(struct request *, struct bio *);
 struct elevator_queue *elevator_alloc(struct request_queue *,
-		struct elevator_type *, struct elevator_tags *);
+		struct elevator_type *, struct elevator_resources *);
 
 /*
  * Helper functions.
-- 
2.51.0