block: kill QUEUE_FLAG_NO_SG_MERGE

Since bdced438acd83ad83a6c ("block: setup bi_phys_segments after splitting"),
physical segment number is mainly figured out in blk_queue_split() for
fast path, and the flag of BIO_SEG_VALID is set there too.

Now only blk_recount_segments() and blk_recalc_rq_segments() use this
flag.

Basically blk_recount_segments() is bypassed in fast path given BIO_SEG_VALID
is set in blk_queue_split().

For another user of blk_recalc_rq_segments():

- run in partial completion branch of blk_update_request, which is an unusual case

- run in blk_cloned_rq_check_limits(), still not a big problem if the flag is killed
since dm-rq is the only user.

Multi-page bvec is enabled now, not doing S/G merging is rather pointless with the
current setup of the I/O path, as it isn't going to save you a significant amount
of cycles.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 1912499..bed0659 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -358,8 +358,7 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
 EXPORT_SYMBOL(blk_queue_split);
 
 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
-                                            struct bio *bio,
-                                            bool no_sg_merge)
+                                            struct bio *bio)
 {
        struct bio_vec bv, bvprv = { NULL };
        int prev = 0;
@@ -385,13 +384,6 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
        nr_phys_segs = 0;
        for_each_bio(bio) {
                bio_for_each_bvec(bv, bio, iter) {
-                       /*
-                        * If SG merging is disabled, each bio vector is
-                        * a segment
-                        */
-                       if (no_sg_merge)
-                               goto new_segment;
-
                        if (prev) {
                                if (seg_size + bv.bv_len
                                    > queue_max_segment_size(q))
@@ -421,27 +413,16 @@ new_segment:
 
 void blk_recalc_rq_segments(struct request *rq)
 {
-       bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
-                       &rq->q->queue_flags);
-
-       rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
-                       no_sg_merge);
+       rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
 }
 
 void blk_recount_segments(struct request_queue *q, struct bio *bio)
 {
-       unsigned short seg_cnt = bio_segments(bio);
-
-       if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
-                       (seg_cnt < queue_max_segments(q)))
-               bio->bi_phys_segments = seg_cnt;
-       else {
-               struct bio *nxt = bio->bi_next;
+       struct bio *nxt = bio->bi_next;
 
-               bio->bi_next = NULL;
-               bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
-               bio->bi_next = nxt;
-       }
+       bio->bi_next = NULL;
+       bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
+       bio->bi_next = nxt;
 
        bio_set_flag(bio, BIO_SEG_VALID);
 }

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index c782e81..697d621 100644 (file)
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -128,7 +128,6 @@ static const char *const blk_queue_flag_name[] = {
        QUEUE_FLAG_NAME(SAME_FORCE),
        QUEUE_FLAG_NAME(DEAD),
        QUEUE_FLAG_NAME(INIT_DONE),
-       QUEUE_FLAG_NAME(NO_SG_MERGE),
        QUEUE_FLAG_NAME(POLL),
        QUEUE_FLAG_NAME(WC),
        QUEUE_FLAG_NAME(FUA),

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 44d471f..fa508ee 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2837,9 +2837,6 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
            set->map[HCTX_TYPE_POLL].nr_queues)
                blk_queue_flag_set(QUEUE_FLAG_POLL, q);
 
-       if (!(set->flags & BLK_MQ_F_SG_MERGE))
-               blk_queue_flag_set(QUEUE_FLAG_NO_SG_MERGE, q);
-
        q->sg_reserved_size = INT_MAX;
 
        INIT_DELAYED_WORK(&q->requeue_work, blk_mq_requeue_work);

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 4b1be75..ba9481f 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1698,14 +1698,6 @@ static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
        return q && !blk_queue_add_random(q);
 }
 
-static int queue_supports_sg_merge(struct dm_target *ti, struct dm_dev *dev,
-                                  sector_t start, sector_t len, void *data)
-{
-       struct request_queue *q = bdev_get_queue(dev->bdev);
-
-       return q && !test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags);
-}
-
 static bool dm_table_all_devices_attribute(struct dm_table *t,
                                           iterate_devices_callout_fn func)
 {
@@ -1902,11 +1894,6 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
        if (!dm_table_supports_write_zeroes(t))
                q->limits.max_write_zeroes_sectors = 0;
 
-       if (dm_table_all_devices_attribute(t, queue_supports_sg_merge))
-               blk_queue_flag_clear(QUEUE_FLAG_NO_SG_MERGE, q);
-       else
-               blk_queue_flag_set(QUEUE_FLAG_NO_SG_MERGE, q);
-
        dm_table_verify_integrity(t);
 
        /*

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index b6292d4..faed9d9 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -588,7 +588,6 @@ struct request_queue {
 #define QUEUE_FLAG_SAME_FORCE  12      /* force complete on same CPU */
 #define QUEUE_FLAG_DEAD                13      /* queue tear-down finished */
 #define QUEUE_FLAG_INIT_DONE   14      /* queue is initialized */
-#define QUEUE_FLAG_NO_SG_MERGE 15      /* don't attempt to merge SG segments*/
 #define QUEUE_FLAG_POLL                16      /* IO polling enabled if set */
 #define QUEUE_FLAG_WC          17      /* Write back caching */
 #define QUEUE_FLAG_FUA         18      /* device supports FUA writes */