[PATCH v3 0/6] blk-mq-tag: remove bt_for_each()

[PATCH v3 0/6] blk-mq-tag: remove bt_for_each()

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

Changes in v3:
  - Document the argument 'q' in the patch which add it.
  - Add Fixes tag and Reviewed-by tags.

Changes in v2:
  - Split by one change per patch and add Fixes tag.
  - Improve commit messages, suggested by Bart Van Assche.

There are two almost identical mechanisms in blk-mq-tag to iterate over
requests of one tags: bt_for_each() and the newer bt_tags_for_each().

This series aim to add support of queue filter in bt_tags_for_each()
then remove bt_for_each(). Fix and update documentation as we're here.

Thanks for review!

Chengming Zhou (6):
  blk-mq-tag: support queue filter in bt_tags_iter()
  blk-mq-tag: introduce __blk_mq_tagset_busy_iter()
  blk-mq-tag: remove bt_for_each()
  blk-mq: delete superfluous check in iterate callback
  blk-mq-tag: fix functions documentation
  blk-mq-tag: fix blk_mq_queue_tag_busy_iter() documentation

 block/blk-mq-tag.c | 176 ++++++++++++---------------------------------
 block/blk-mq.c     |  12 ++--
 2 files changed, 49 insertions(+), 139 deletions(-)

-- 
2.41.0

[PATCH v3 1/6] blk-mq-tag: support queue filter in bt_tags_iter()

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

The only user of bt_for_each() is blk_mq_queue_tag_busy_iter(), which
need to filter queue when iterate the tags. In preparation of removing
bt_for_each(), support queue filter in bt_tags_iter().

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq-tag.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index cc57e2dd9a0b..3cf3cf72cd54 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -329,6 +329,7 @@ struct bt_tags_iter_data {
 	busy_tag_iter_fn *fn;
 	void *data;
 	unsigned int flags;
+	struct request_queue *q;
 };
 
 #define BT_TAG_ITER_RESERVED		(1 << 0)
@@ -357,9 +358,13 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 	if (!rq)
 		return true;
 
+	if (iter_data->q && iter_data->q != rq->q)
+		goto out;
+
 	if (!(iter_data->flags & BT_TAG_ITER_STARTED) ||
 	    blk_mq_request_started(rq))
 		ret = iter_data->fn(rq, iter_data->data);
+out:
 	if (!iter_static_rqs)
 		blk_mq_put_rq_ref(rq);
 	return ret;
-- 
2.41.0

[PATCH v3 2/6] blk-mq-tag: introduce __blk_mq_tagset_busy_iter()

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

For support of specified queue filter when iterating over a tagset,
we introduce __blk_mq_tagset_busy_iter() here and all current users
just set queue as NULL which means have no queue filter.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq-tag.c | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 3cf3cf72cd54..dc4edde3c80a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -381,15 +381,18 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
  *		to continue iterating tags, false to stop.
  * @data:	Will be passed as second argument to @fn.
  * @flags:	BT_TAG_ITER_*
+ * @q:		Only iterate over requests of this queue.
  */
 static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
-			     busy_tag_iter_fn *fn, void *data, unsigned int flags)
+			     busy_tag_iter_fn *fn, void *data, unsigned int flags,
+			     struct request_queue *q)
 {
 	struct bt_tags_iter_data iter_data = {
 		.tags = tags,
 		.fn = fn,
 		.data = data,
 		.flags = flags,
+		.q = q,
 	};
 
 	if (tags->rqs)
@@ -397,14 +400,15 @@ static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
 }
 
 static void __blk_mq_all_tag_iter(struct blk_mq_tags *tags,
-		busy_tag_iter_fn *fn, void *priv, unsigned int flags)
+		busy_tag_iter_fn *fn, void *priv, unsigned int flags,
+		struct request_queue *q)
 {
 	WARN_ON_ONCE(flags & BT_TAG_ITER_RESERVED);
 
 	if (tags->nr_reserved_tags)
 		bt_tags_for_each(tags, &tags->breserved_tags, fn, priv,
-				 flags | BT_TAG_ITER_RESERVED);
-	bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, flags);
+				 flags | BT_TAG_ITER_RESERVED, q);
+	bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, flags, q);
 }
 
 /**
@@ -422,7 +426,23 @@ static void __blk_mq_all_tag_iter(struct blk_mq_tags *tags,
 void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
 		void *priv)
 {
-	__blk_mq_all_tag_iter(tags, fn, priv, BT_TAG_ITER_STATIC_RQS);
+	__blk_mq_all_tag_iter(tags, fn, priv, BT_TAG_ITER_STATIC_RQS, NULL);
+}
+
+static void __blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
+				      busy_tag_iter_fn *fn, void *priv,
+				      struct request_queue *q)
+{
+	unsigned int flags = tagset->flags;
+	int i, nr_tags;
+
+	nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
+
+	for (i = 0; i < nr_tags; i++) {
+		if (tagset->tags && tagset->tags[i])
+			__blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
+					      BT_TAG_ITER_STARTED, q);
+	}
 }
 
 /**
@@ -441,16 +461,7 @@ void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 		busy_tag_iter_fn *fn, void *priv)
 {
-	unsigned int flags = tagset->flags;
-	int i, nr_tags;
-
-	nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
-
-	for (i = 0; i < nr_tags; i++) {
-		if (tagset->tags && tagset->tags[i])
-			__blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
-					      BT_TAG_ITER_STARTED);
-	}
+	__blk_mq_tagset_busy_iter(tagset, fn, priv, NULL);
 }
 EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
 
-- 
2.41.0

[PATCH v3 3/6] blk-mq-tag: remove bt_for_each()

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

Change the only user of bt_for_each() to use the introduced function
__blk_mq_tagset_busy_iter() to specify queue filter when iterating.

Since blk_mq_queue_tag_busy_iter() is only used to iterate over started
requests, __blk_mq_tagset_busy_iter() already have BT_TAG_ITER_STARTED
filter to iterate over started requests only, there should be no
problem.

Only one potential disadvantage I can see is that we lost the
blk_mq_hw_queue_mapped() filter, which maybe not happen for now.
Unmapped hctx was used to dynamically map or unmap when CPU hotplug,
but we don't do this anymore, we always map all possible CPUs now.
So it seems unmapped hctx may only happen if something wrong with
driver's tagset map settings.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq-tag.c | 99 +---------------------------------------------
 1 file changed, 1 insertion(+), 98 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index dc4edde3c80a..3ddc0c7b7f7e 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -241,14 +241,6 @@ void blk_mq_put_tags(struct blk_mq_tags *tags, int *tag_array, int nr_tags)
 					tag_array, nr_tags);
 }
 
-struct bt_iter_data {
-	struct blk_mq_hw_ctx *hctx;
-	struct request_queue *q;
-	busy_tag_iter_fn *fn;
-	void *data;
-	bool reserved;
-};
-
 static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
 		unsigned int bitnr)
 {
@@ -263,67 +255,6 @@ static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
 	return rq;
 }
 
-static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
-{
-	struct bt_iter_data *iter_data = data;
-	struct blk_mq_hw_ctx *hctx = iter_data->hctx;
-	struct request_queue *q = iter_data->q;
-	struct blk_mq_tag_set *set = q->tag_set;
-	struct blk_mq_tags *tags;
-	struct request *rq;
-	bool ret = true;
-
-	if (blk_mq_is_shared_tags(set->flags))
-		tags = set->shared_tags;
-	else
-		tags = hctx->tags;
-
-	if (!iter_data->reserved)
-		bitnr += tags->nr_reserved_tags;
-	/*
-	 * We can hit rq == NULL here, because the tagging functions
-	 * test and set the bit before assigning ->rqs[].
-	 */
-	rq = blk_mq_find_and_get_req(tags, bitnr);
-	if (!rq)
-		return true;
-
-	if (rq->q == q && (!hctx || rq->mq_hctx == hctx))
-		ret = iter_data->fn(rq, iter_data->data);
-	blk_mq_put_rq_ref(rq);
-	return ret;
-}
-
-/**
- * bt_for_each - iterate over the requests associated with a hardware queue
- * @hctx:	Hardware queue to examine.
- * @q:		Request queue to examine.
- * @bt:		sbitmap to examine. This is either the breserved_tags member
- *		or the bitmap_tags member of struct blk_mq_tags.
- * @fn:		Pointer to the function that will be called for each request
- *		associated with @hctx that has been assigned a driver tag.
- *		@fn will be called as follows: @fn(@hctx, rq, @data, @reserved)
- *		where rq is a pointer to a request. Return true to continue
- *		iterating tags, false to stop.
- * @data:	Will be passed as third argument to @fn.
- * @reserved:	Indicates whether @bt is the breserved_tags member or the
- *		bitmap_tags member of struct blk_mq_tags.
- */
-static void bt_for_each(struct blk_mq_hw_ctx *hctx, struct request_queue *q,
-			struct sbitmap_queue *bt, busy_tag_iter_fn *fn,
-			void *data, bool reserved)
-{
-	struct bt_iter_data iter_data = {
-		.hctx = hctx,
-		.fn = fn,
-		.data = data,
-		.reserved = reserved,
-		.q = q,
-	};
-
-	sbitmap_for_each_set(&bt->sb, bt_iter, &iter_data);
-}
-
 struct bt_tags_iter_data {
 	struct blk_mq_tags *tags;
 	busy_tag_iter_fn *fn;
@@ -520,35 +451,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
 	if (!percpu_ref_tryget(&q->q_usage_counter))
 		return;
 
-	if (blk_mq_is_shared_tags(q->tag_set->flags)) {
-		struct blk_mq_tags *tags = q->tag_set->shared_tags;
-		struct sbitmap_queue *bresv = &tags->breserved_tags;
-		struct sbitmap_queue *btags = &tags->bitmap_tags;
-
-		if (tags->nr_reserved_tags)
-			bt_for_each(NULL, q, bresv, fn, priv, true);
-		bt_for_each(NULL, q, btags, fn, priv, false);
-	} else {
-		struct blk_mq_hw_ctx *hctx;
-		unsigned long i;
-
-		queue_for_each_hw_ctx(q, hctx, i) {
-			struct blk_mq_tags *tags = hctx->tags;
-			struct sbitmap_queue *bresv = &tags->breserved_tags;
-			struct sbitmap_queue *btags = &tags->bitmap_tags;
-
-			/*
-			 * If no software queues are currently mapped to this
-			 * hardware queue, there's nothing to check
-			 */
-			if (!blk_mq_hw_queue_mapped(hctx))
-				continue;
-
-			if (tags->nr_reserved_tags)
-				bt_for_each(hctx, q, bresv, fn, priv, true);
-			bt_for_each(hctx, q, btags, fn, priv, false);
-		}
-	}
+	__blk_mq_tagset_busy_iter(q->tag_set, fn, priv, q);
 	blk_queue_exit(q);
 }
 
-- 
2.41.0

[PATCH v3 4/6] blk-mq: delete superfluous check in iterate callback

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

The previous patch in this series changed the behavior of
blk_mq_queue_tag_busy_iter() from iterating over all allocated tags into
iterating over started requests only. Leave out the code from
blk_mq_rq_inflight() that became superfluous because of this change.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 953f08354c8c..f1bafbae0a61 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1516,19 +1516,15 @@ EXPORT_SYMBOL(blk_mq_delay_kick_requeue_list);
 
 static bool blk_mq_rq_inflight(struct request *rq, void *priv)
 {
+	bool *busy = priv;
+
 	/*
 	 * If we find a request that isn't idle we know the queue is busy
 	 * as it's checked in the iter.
 	 * Return false to stop the iteration.
 	 */
-	if (blk_mq_request_started(rq)) {
-		bool *busy = priv;
-
-		*busy = true;
-		return false;
-	}
-
-	return true;
+	*busy = true;
+	return false;
 }
 
 bool blk_mq_queue_inflight(struct request_queue *q)
-- 
2.41.0

[PATCH v3 5/6] blk-mq-tag: fix functions documentation

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

There are some stale functions documentation in blk-mq-tag, since
the prototype of busy_tag_iter_fn() has changed. Fix it as we're here.

Fixes: 2dd6532e9591 ("blk-mq: Drop 'reserved' arg of busy_tag_iter_fn")
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq-tag.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 3ddc0c7b7f7e..0d42f3c4d76e 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -307,9 +307,9 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
  * @bt:		sbitmap to examine. This is either the breserved_tags member
  *		or the bitmap_tags member of struct blk_mq_tags.
  * @fn:		Pointer to the function that will be called for each started
- *		request. @fn will be called as follows: @fn(rq, @data,
- *		@reserved) where rq is a pointer to a request. Return true
- *		to continue iterating tags, false to stop.
+ *		request. @fn will be called as follows: @fn(rq, @data) where
+ *		rq is a pointer to a request. Return true to continue iterating
+ *		tags, false to stop.
  * @data:	Will be passed as second argument to @fn.
  * @flags:	BT_TAG_ITER_*
  * @q:		Only iterate over requests of this queue.
@@ -346,10 +346,9 @@ static void __blk_mq_all_tag_iter(struct blk_mq_tags *tags,
  * blk_mq_all_tag_iter - iterate over all requests in a tag map
  * @tags:	Tag map to iterate over.
  * @fn:		Pointer to the function that will be called for each
- *		request. @fn will be called as follows: @fn(rq, @priv,
- *		reserved) where rq is a pointer to a request. 'reserved'
- *		indicates whether or not @rq is a reserved request. Return
- *		true to continue iterating tags, false to stop.
+ *		request. @fn will be called as follows: @fn(rq, @priv)
+ *		where rq is a pointer to a request. Return true to
+ *		continue iterating tags, false to stop.
  * @priv:	Will be passed as second argument to @fn.
  *
  * Caller has to pass the tag map from which requests are allocated.
@@ -380,10 +379,9 @@ static void __blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
  * blk_mq_tagset_busy_iter - iterate over all started requests in a tag set
  * @tagset:	Tag set to iterate over.
  * @fn:		Pointer to the function that will be called for each started
- *		request. @fn will be called as follows: @fn(rq, @priv,
- *		reserved) where rq is a pointer to a request. 'reserved'
- *		indicates whether or not @rq is a reserved request. Return
- *		true to continue iterating tags, false to stop.
+ *		request. @fn will be called as follows: @fn(rq, @priv)
+ *		where rq is a pointer to a request. Return true to
+ *		continue iterating tags, false to stop.
  * @priv:	Will be passed as second argument to @fn.
  *
  * We grab one request reference before calling @fn and release it after
@@ -430,11 +428,9 @@ EXPORT_SYMBOL(blk_mq_tagset_wait_completed_request);
  * blk_mq_queue_tag_busy_iter - iterate over all requests with a driver tag
  * @q:		Request queue to examine.
  * @fn:		Pointer to the function that will be called for each request
- *		on @q. @fn will be called as follows: @fn(hctx, rq, @priv,
- *		reserved) where rq is a pointer to a request and hctx points
- *		to the hardware queue associated with the request. 'reserved'
- *		indicates whether or not @rq is a reserved request.
- * @priv:	Will be passed as third argument to @fn.
+ *		on @q. @fn will be called as follows: @fn(rq, @priv) where rq
+ *		is a pointer to a request.
+ * @priv:	Will be passed as second argument to @fn.
  *
  * Note: if @q->tag_set is shared with other request queues then @fn will be
  * called for all requests on all queues that share that tag set and not only
-- 
2.41.0

[PATCH v3 6/6] blk-mq-tag: fix blk_mq_queue_tag_busy_iter() documentation

[chengming.zhou]

From: Chengming Zhou <zhouchengming@bytedance.com>

The blk_mq_queue_tag_busy_iter() is only used to iterate over reqeusts
of the specified queue, fix the documentation.

Fixes: c7b1bf5cca76 ("blk-mq: Document the functions that iterate over requests")
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 block/blk-mq-tag.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 0d42f3c4d76e..69b156750559 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -433,8 +433,7 @@ EXPORT_SYMBOL(blk_mq_tagset_wait_completed_request);
  * @priv:	Will be passed as second argument to @fn.
  *
  * Note: if @q->tag_set is shared with other request queues then @fn will be
- * called for all requests on all queues that share that tag set and not only
- * for requests associated with @q.
+ * called only for requests associated with @q.
  */
 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
 		void *priv)
-- 
2.41.0

Re: [PATCH v3 6/6] blk-mq-tag: fix blk_mq_queue_tag_busy_iter() documentation

[Bart Van Assche]

On 8/23/23 08:18, chengming.zhou@linux.dev wrote:
> The blk_mq_queue_tag_busy_iter() is only used to iterate over reqeusts
> of the specified queue, fix the documentation.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Re: [PATCH v3 0/6] blk-mq-tag: remove bt_for_each()

[Chengming Zhou]

On 2023/8/23 23:17, chengming.zhou@linux.dev wrote:
> From: Chengming Zhou <zhouchengming@bytedance.com>
> 
> Changes in v3:
>   - Document the argument 'q' in the patch which add it.
>   - Add Fixes tag and Reviewed-by tags.

Hello, gentle ping.

Thanks.

> 
> Changes in v2:
>   - Split by one change per patch and add Fixes tag.
>   - Improve commit messages, suggested by Bart Van Assche.
> 
> There are two almost identical mechanisms in blk-mq-tag to iterate over
> requests of one tags: bt_for_each() and the newer bt_tags_for_each().
> 
> This series aim to add support of queue filter in bt_tags_for_each()
> then remove bt_for_each(). Fix and update documentation as we're here.
> 
> Thanks for review!
> 
> Chengming Zhou (6):
>   blk-mq-tag: support queue filter in bt_tags_iter()
>   blk-mq-tag: introduce __blk_mq_tagset_busy_iter()
>   blk-mq-tag: remove bt_for_each()
>   blk-mq: delete superfluous check in iterate callback
>   blk-mq-tag: fix functions documentation
>   blk-mq-tag: fix blk_mq_queue_tag_busy_iter() documentation
> 
>  block/blk-mq-tag.c | 176 ++++++++++++---------------------------------
>  block/blk-mq.c     |  12 ++--
>  2 files changed, 49 insertions(+), 139 deletions(-)
> 

Re: [PATCH v3 0/6] blk-mq-tag: remove bt_for_each()

[Bart Van Assche]

On 9/2/23 07:58, Chengming Zhou wrote:
> Hello, gentle ping.
According to 
https://lore.kernel.org/linux-kernel/CAHk-=wgmKhCrdrOCjp=5v9NO6C=PJ8ZTZcCXj09piHzsZ7qqmw@mail.gmail.com/,
the merge window opened on August 27 (one week ago). Since we are now
in the middle of the merge window and since maintainers typically do
not merge patch series during the merge window, it's probably the wrong
time to send a ping.

Thanks,

Bart.

Re: [PATCH v3 0/6] blk-mq-tag: remove bt_for_each()

[Chengming Zhou]

On 2023/9/4 07:51, Bart Van Assche wrote:
> On 9/2/23 07:58, Chengming Zhou wrote:
>> Hello, gentle ping.
> According to https://lore.kernel.org/linux-kernel/CAHk-=wgmKhCrdrOCjp=5v9NO6C=PJ8ZTZcCXj09piHzsZ7qqmw@mail.gmail.com/,
> the merge window opened on August 27 (one week ago). Since we are now
> in the middle of the merge window and since maintainers typically do
> not merge patch series during the merge window, it's probably the wrong
> time to send a ping.
> 

Oh, I get it. Sorry for the noise.

Thanks.