From: Christoph Hellwig <hch@lst.de>
Date: Wed, 2 Feb 2022 17:01:04 +0100
Subject: [PATCH] dm: simplify the single bio fast path in
 __send_duplicate_bios
Git-commit: 891fced644a7529bfd4b1436b2341527ce8f68ad
Patch-mainline: v5.18-rc1
References: jsc#PED-1183

Most targets just need a single flush bio.  Open code that case in
__send_duplicate_bios without the need to add the bio to a list.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Link: https://lore.kernel.org/r/20220202160109.108149-9-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/md/dm.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c05b6ff1bb95..78df75f57288 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1241,15 +1241,6 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
 	struct bio *bio;
 	int try;
 
-	if (!num_bios)
-		return;
-
-	if (num_bios == 1) {
-		bio = alloc_tio(ci, ti, 0, len, GFP_NOIO);
-		bio_list_add(blist, bio);
-		return;
-	}
-
 	for (try = 0; try < 2; try++) {
 		int bio_nr;
 
@@ -1279,12 +1270,23 @@ static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
 	struct bio_list blist = BIO_EMPTY_LIST;
 	struct bio *clone;
 
-	alloc_multiple_bios(&blist, ci, ti, num_bios, len);
-
-	while ((clone = bio_list_pop(&blist))) {
+	switch (num_bios) {
+	case 0:
+		break;
+	case 1:
+		clone = alloc_tio(ci, ti, 0, len, GFP_NOIO);
 		if (len)
 			bio_setup_sector(clone, ci->sector, *len);
 		__map_bio(clone);
+		break;
+	default:
+		alloc_multiple_bios(&blist, ci, ti, num_bios, len);
+		while ((clone = bio_list_pop(&blist))) {
+			if (len)
+				bio_setup_sector(clone, ci->sector, *len);
+			__map_bio(clone);
+		}
+		break;
 	}
 }
 
-- 
2.35.3