Re: [PATCH 1/2] block: modify blk_mq_plug() to allow only reads for zoned block devices

[Pankaj Raghav <p.raghav@samsung.com>]

On 2022-09-27 18:52, Jens Axboe wrote:
>> Well, the only opcodes we do zone locking for is REQ_OP_WRITE and
>> REQ_OP_WRITE_ZEROES.  So this should be:
>>
>> 	if (zoned && (op == REQ_OP_WRITE || op == REQ_OP_WRITE_ZEROES))
>> 		return NULL;
> 
> I'd rather just make it explicit and use that. Pankaj, do you want
> to spin a v2 with that?
> 

Based on all the suggestions:

block: adapt blk_mq_plug() to not plug for writes that require a zone lock

The current implementation of blk_mq_plug() disables plugging for all
operations that involves a transfer to the device as we just check if
the last bit in op_is_write() function.

Modify blk_mq_plug() to disable plugging only for REQ_OP_WRITE and
REQ_OP_WRITE_ZEROS as they might require a zone lock.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>

diff --git a/block/blk-mq.h b/block/blk-mq.h
index 8ca453ac243d..297289cdd521 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -312,7 +312,8 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
 static inline struct blk_plug *blk_mq_plug( struct bio *bio)
 {
 	/* Zoned block device write operation case: do not plug the BIO */
-	if (bdev_is_zoned(bio->bi_bdev) && op_is_write(bio_op(bio)))
+	if (IS_ENABLED(CONFIG_BLK_DEV_ZONED) &&
+	    blk_op_is_zoned_write(bio->bi_bdev, bio_op(bio)))
 		return NULL;

 	/*
diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index a264621d4905..fa926424edb6 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -63,13 +63,10 @@ bool blk_req_needs_zone_write_lock(struct request *rq)
 	if (!rq->q->disk->seq_zones_wlock)
 		return false;

-	switch (req_op(rq)) {
-	case REQ_OP_WRITE_ZEROES:
-	case REQ_OP_WRITE:
+	if (blk_op_is_zoned_write(rq->q->disk->part0, req_op(rq)))
 		return blk_rq_zone_is_seq(rq);
-	default:
-		return false;
-	}
+
+	return false;
 }
 EXPORT_SYMBOL_GPL(blk_req_needs_zone_write_lock);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8038c5fbde40..719025028fa4 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1300,6 +1300,15 @@ static inline bool bdev_is_zoned(struct block_device *bdev)
 	return false;
 }

+static inline bool blk_op_is_zoned_write(struct block_device *bdev,
+					 blk_opf_t op)
+{
+	if (!bdev_is_zoned(bdev))
+		return false;
+
+	return op == REQ_OP_WRITE || op == REQ_OP_WRITE_ZEROES;
+}
+
 static inline sector_t bdev_zone_sectors(struct block_device *bdev)
 {
 	struct request_queue *q = bdev_get_queue(bdev);


Does this look fine?