Re: [PATCH 04/11] blk-mq: Facilitate a shared sbitmap per tagset

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@@ -483,8 +483,8 @@ static int hctx_tags_bitmap_show(void *data, struct seq_file *m)
  	res = mutex_lock_interruptible(&q->sysfs_lock);
  	if (res)
  		goto out;
-	if (hctx->tags)
-		sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);
+	if (hctx->tags) /* We should just iterate the relevant bits for this hctx FIXME */

Bart's solution to this problem seemed ok, if he doesn't mind us borrowing his idea:

https://lore.kernel.org/linux-block/5183ab13-0c81-95f0-95ba-40318569c6c6@xxxxxxxxxx/T/#m24394fe70b1ea79a154dfd9620f5e553c3e7e7da

See hctx_tags_bitmap_show().

It might be also reasonable to put that in another follow on patch, as there would be no enablers of the "shared" bitmap until later patches.

+		sbitmap_bitmap_show(&hctx->tags->bitmap_tags->sb, m);
  	mutex_unlock(&q->sysfs_lock);
out:
@@ -518,7 +518,7 @@ static int hctx_sched_tags_bitmap_show(void *data, struct seq_file *m)
  	if (res)
  		goto out;
  	if (hctx->sched_tags)
-		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags.sb, m);
+		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags->sb, m);
  	mutex_unlock(&q->sysfs_lock);
out:
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ca22afd47b3d..1855f8f5edd4 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -492,6 +492,7 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q)
int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
  {
+	struct blk_mq_tag_set *tag_set = q->tag_set;
  	struct blk_mq_hw_ctx *hctx;
  	struct elevator_queue *eq;
  	unsigned int i;
@@ -537,6 +538,19 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
  		blk_mq_debugfs_register_sched_hctx(q, hctx);
  	}
+ if (blk_mq_is_sbitmap_shared(tag_set)) {
+		if (!blk_mq_init_sched_shared_sbitmap(tag_set, q->nr_requests)) {
+			ret = -ENOMEM;
+			goto err;
+		}
+		queue_for_each_hw_ctx(q, hctx, i) {
+			struct blk_mq_tags *tags = hctx->sched_tags;
+
+			tags->bitmap_tags = &tag_set->__sched_bitmap_tags;
+			tags->breserved_tags = &tag_set->__sched_breserved_tags;
+		}
+	}
+
  	return 0;
err:
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index f5009587e1b5..2e714123e846 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -20,7 +20,7 @@ bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
  	if (!tags)
  		return true;
- return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);
+	return sbitmap_any_bit_clear(&tags->bitmap_tags->sb);
  }
/*
@@ -43,9 +43,9 @@ bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
   */
  void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
  {
-	sbitmap_queue_wake_all(&tags->bitmap_tags);
+	sbitmap_queue_wake_all(tags->bitmap_tags);
  	if (include_reserve)
-		sbitmap_queue_wake_all(&tags->breserved_tags);
+		sbitmap_queue_wake_all(tags->breserved_tags);
  }
/*
@@ -121,10 +121,10 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
  			WARN_ON_ONCE(1);
  			return BLK_MQ_TAG_FAIL;
  		}
-		bt = &tags->breserved_tags;
+		bt = tags->breserved_tags;

We could put all of this in an earlier patch (as you had in v4, modulo dynamic memory part), which would be easier to review and get accepted.

  		tag_offset = 0;
  	} else {
-		bt = &tags->bitmap_tags;
+		bt = tags->bitmap_tags;
  		tag_offset = tags->nr_reserved_tags;
  	}


[...]

  	if (!set)
@@ -3160,6 +3179,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
  			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
  							false);
  		} else {
+			sched_tags = true;
  			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
  							nr, true);
  		}
@@ -3169,8 +3189,43 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
  			q->elevator->type->ops.depth_updated(hctx);
  	}
- if (!ret)
+	/*
+	 * if ret is 0, all queues should have been updated to the same depth
+	 * if not, then maybe some have been updated - yuk, need to handle this for shared sbitmap...
+	 * if some are updated, we should probably roll back the change altogether. FIXME
+	 */

If you don't have a shared sched bitmap - which I didn't think we needed - then all we need is a simple sbitmap_queue_resize(&tagset->__bitmap_tags)

Otherwise it's horrible to resize shared sched bitmaps...

+	if (!ret) {
+		if (blk_mq_is_sbitmap_shared(set)) {
+			if (sched_tags) {
+				blk_mq_exit_shared_sched_sbitmap(set);
+				if (!blk_mq_init_sched_shared_sbitmap(set, nr))
+					return -ENOMEM; /* fixup error handling */
+
+				queue_for_each_hw_ctx(q, hctx, i) {
+					hctx->sched_tags->bitmap_tags =
+						&set->__sched_bitmap_tags;
+					hctx->sched_tags->breserved_tags =
+						&set->__sched_breserved_tags;
+				}
+			} else {
+				blk_mq_exit_shared_sbitmap(set);
+				if (!blk_mq_init_shared_sbitmap(set))
+					return -ENOMEM; /* fixup error handling */
+
+				queue_for_each_hw_ctx(q, hctx, i) {
+					hctx->tags->bitmap_tags =
+						&set->__bitmap_tags;
+					hctx->tags->breserved_tags =
+						&set->__breserved_tags;
+				}
+			}
+		}
  		q->nr_requests = nr;
+	}
+	/*
+	 * if ret != 0, q->nr_requests would not be updated, yet the depth
+	 * for some hctx may have changed - is that right?
+	 */
blk_mq_unquiesce_queue(q);
  	blk_mq_unfreeze_queue(q);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 78d38b5f2793..4c1ea206d3f4 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -166,6 +166,11 @@ struct blk_mq_alloc_data {
  	struct blk_mq_hw_ctx *hctx;
  };
+static inline bool blk_mq_is_sbitmap_shared(struct blk_mq_tag_set *tag_set)
+{
+	return !!(tag_set->flags & BLK_MQ_F_TAG_HCTX_SHARED);

Bart already gave some comments on this

+}
+
  static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data *data)
  {
  	if (data->flags & BLK_MQ_REQ_INTERNAL)
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 34dcea0ef637..a7a537501d70 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -359,7 +359,7 @@ static unsigned int kyber_sched_tags_shift(struct request_queue *q)
  	 * All of the hardware queues have the same depth, so we can just grab
  	 * the shift of the first one.
  	 */
-	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
+	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;
  }
static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
@@ -502,7 +502,7 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
  	khd->batching = 0;
hctx->sched_data = khd;
-	sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,
+	sbitmap_queue_min_shallow_depth(hctx->sched_tags->bitmap_tags,
  					kqd->async_depth);
return 0;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 147185394a25..10c9ed3dbe80 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -109,6 +109,12 @@ struct blk_mq_tag_set {
  	unsigned int		flags;		/* BLK_MQ_F_* */
  	void			*driver_data;
+ struct sbitmap_queue __bitmap_tags;
+	struct sbitmap_queue	__breserved_tags;
+
+	struct sbitmap_queue	__sched_bitmap_tags;
+	struct sbitmap_queue	__sched_breserved_tags;
+
  	struct blk_mq_tags	**tags;
struct mutex tag_list_lock;
@@ -226,6 +232,9 @@ struct blk_mq_ops {
  enum {
  	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
  	BLK_MQ_F_TAG_QUEUE_SHARED	= 1 << 1,
+	BLK_MQ_F_TAG_HCTX_SHARED	= 1 << 2,
+	BLK_MQ_F_TAG_BITMAP_ALLOCATED	= 1 << 3,
+	BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED = 1 << 4,
  	BLK_MQ_F_BLOCKING	= 1 << 5,
  	BLK_MQ_F_NO_SCHED	= 1 << 6,
  	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,





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