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block: kill QUEUE_FLAG_NO_SG_MERGE

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Since bdced438ac ("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>
This commit is contained in:
Ming Lei 2019-02-15 19:13:23 +08:00 committed by Jens Axboe
parent ac4fa1d107
commit 2705c93742
5 changed files with 6 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
block/blk-merge.c
View File

@ -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);
struct bio *nxt = bio->bi_next;
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;
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);
}

1
block/blk-mq-debugfs.c
View File

@ -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),

3
block/blk-mq.c
View File

@ -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);

13
drivers/md/dm-table.c
View File

@ -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);
/*

1
include/linux/blkdev.h
View File

@ -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 */