From: Mikulas Patocka <mpatocka@redhat.com>
Date: Sat, 23 Jan 2021 09:19:56 -0500
Subject: [PATCH] dm writecache: fix performance degradation in ssd mode
Git-commit: cb728484a7710c202f02b96aa0962ce9b07aa5c2
Patch-mainline: v5.12-rc1
References: git-fixes

Fix a thinko in ssd_commit_superblock. region.count is in sectors, not
bytes. This bug doesn't corrupt data, but it causes performance
degradation.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: dc8a01ae1dbd ("dm writecache: optimize superblock write")
Cc: stable@vger.kernel.org # v5.7+
Reported-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 drivers/md/dm-writecache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index d5223a0e5cc5..1769653c3d6b 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -523,7 +523,7 @@ static void ssd_commit_superblock(struct dm_writecache *wc)
 
 	region.bdev = wc->ssd_dev->bdev;
 	region.sector = 0;
-	region.count = PAGE_SIZE;
+	region.count = PAGE_SIZE >> SECTOR_SHIFT;
 
 	if (unlikely(region.sector + region.count > wc->metadata_sectors))
 		region.count = wc->metadata_sectors - region.sector;
-- 
2.29.2