[PATCH 5.10 645/663] dm writecache: fix performance degradation in ssd mode

[Greg Kroah-Hartman]

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit cb728484a7710c202f02b96aa0962ce9b07aa5c2 upstream.

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@xxxxxxxxxx>
Fixes: dc8a01ae1dbd ("dm writecache: optimize superblock write")
Cc: stable@xxxxxxxxxxxxxxx # v5.7+
Reported-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/md/dm-writecache.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -523,7 +523,7 @@ static void ssd_commit_superblock(struct
 
 	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;