On Thu, Jan 12 2017, Bart Van Assche wrote:

On Wed, 2017-01-11 at 14:40 -0700, Jens Axboe wrote:

quoted

@@ -451,11 +456,11 @@ void blk_insert_flush(struct request *rq)
 	 * processed directly without going through flush machinery.  Queue
 	 * for normal execution.
 	 */
-	if ((policy & REQ_FSEQ_DATA) &&
-	    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
-		if (q->mq_ops) {
-			blk_mq_insert_request(rq, false, true, false);
-		} else
+	if (((policy & REQ_FSEQ_DATA) &&
+	     !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH)))) {
+		if (q->mq_ops)
+			blk_mq_sched_insert_request(rq, false, true, false);
+		else
 			list_add_tail(&rq->queuelist, &q->queue_head);
 		return;
 	}

Not that it really matters, but this change adds a pair of parentheses --
"if (e)" is changed into "if ((e))". Is this necessary?

I fixed that up earlier today, as I noticed the same. So that's gone in
the current -git tree.

quoted

+void blk_mq_sched_free_hctx_data(struct request_queue *q,
+				 void (*exit)(struct blk_mq_hw_ctx *))
+{
+	struct blk_mq_hw_ctx *hctx;
+	int i;
+
+	queue_for_each_hw_ctx(q, hctx, i) {
+		if (exit)
+			exit(hctx);
+		kfree(hctx->sched_data);
+		hctx->sched_data = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
+
+int blk_mq_sched_init_hctx_data(struct request_queue *q, size_t size,
+				int (*init)(struct blk_mq_hw_ctx *),
+				void (*exit)(struct blk_mq_hw_ctx *))
+{
+	struct blk_mq_hw_ctx *hctx;
+	int ret;
+	int i;
+
+	queue_for_each_hw_ctx(q, hctx, i) {
+		hctx->sched_data = kmalloc_node(size, GFP_KERNEL, hctx->numa_node);
+		if (!hctx->sched_data) {
+			ret = -ENOMEM;
+			goto error;
+		}
+
+		if (init) {
+			ret = init(hctx);
+			if (ret) {
+				/*
+				 * We don't want to give exit() a partially
+				 * initialized sched_data. init() must clean up
+				 * if it fails.
+				 */
+				kfree(hctx->sched_data);
+				hctx->sched_data = NULL;
+				goto error;
+			}
+		}
+	}
+
+	return 0;
+error:
+	blk_mq_sched_free_hctx_data(q, exit);
+	return ret;
+}

If one of the init() calls by blk_mq_sched_init_hctx_data() fails then
blk_mq_sched_free_hctx_data() will call exit() even for hctx's for which
init() has not been called. How about changing "if (exit)" into "if (exit &&
hctx->sched_data)" such that exit() is only called for hctx's for which
init() has been called?

Good point, I'll make that change to the exit function.

quoted

+struct request *blk_mq_sched_get_request(struct request_queue *q,
+					 struct bio *bio,
+					 unsigned int op,
+					 struct blk_mq_alloc_data *data)
+{
+	struct elevator_queue *e = q->elevator;
+	struct blk_mq_hw_ctx *hctx;
+	struct blk_mq_ctx *ctx;
+	struct request *rq;
+
+	blk_queue_enter_live(q);
+	ctx = blk_mq_get_ctx(q);
+	hctx = blk_mq_map_queue(q, ctx->cpu);
+
+	blk_mq_set_alloc_data(data, q, 0, ctx, hctx);
+
+	if (e) {
+		data->flags |= BLK_MQ_REQ_INTERNAL;
+		if (e->type->ops.mq.get_request)
+			rq = e->type->ops.mq.get_request(q, op, data);
+		else
+			rq = __blk_mq_alloc_request(data, op);
+	} else {
+		rq = __blk_mq_alloc_request(data, op);
+		if (rq) {
+			rq->tag = rq->internal_tag;
+			rq->internal_tag = -1;
+		}
+	}
+
+	if (rq) {
+		rq->elv.icq = NULL;
+		if (e && e->type->icq_cache)
+			blk_mq_sched_assign_ioc(q, rq, bio);
+		data->hctx->queued++;
+		return rq;
+	}
+
+	blk_queue_exit(q);
+	return NULL;
+}

The "rq->tag = rq->internal_tag; rq->internal_tag = -1;" occurs not only
here but also in blk_mq_alloc_request_hctx(). Has it been considered to move
that code into __blk_mq_alloc_request()?

Yes, it's in two locations. I wanted to keep it out of
__blk_mq_alloc_request(), so we can still use that for normal tag
allocations. But maybe it's better for __blk_mq_alloc_request() to just
do:

        if (flags & BLK_MQ_REQ_INTERNAL) {
                rq->tag = -1;
                rq->internal_tag = tag;
        } else {
                rq->tag = tag;
                rq->internal_tag = -1;
        }

and handle it directly in there. What do you think?

Hah, nevermind, I should have read further. I guess we agree, I'll make
that change.

quoted

@@ -313,6 +313,9 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, int rw,
 		goto out_queue_exit;
 	}
 
+	rq->tag = rq->internal_tag;
+	rq->internal_tag = -1;
+
 	return rq;
 
 out_queue_exit:

@@ -321,10 +324,10 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, int rw,
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);

Should something like "WARN_ON_ONCE(flags & BLK_MQ_REQ_INTERNAL)" be added
at the start of this function to avoid that BLK_MQ_REQ_INTERNAL is passed in
from outside the block layer?

Yes, seems like a prudent safety check. I'll add it, thanks.

-- 
Jens Axboe