linux-kernel - [PATCH 5.11 757/775] dm writecache: fix performance degradation in ssd mode

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Date:   Mon,  1 Mar 2021 17:15:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mikulas Patocka <mpatocka@...hat.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 5.11 757/775] dm writecache: fix performance degradation in ssd mode

From: Mikulas Patocka <mpatocka@...hat.com>

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@...hat.com>
Fixes: dc8a01ae1dbd ("dm writecache: optimize superblock write")
Cc: stable@...r.kernel.org # v5.7+
Reported-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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;