linux-kernel - [PATCH 5.12 235/242] dm writecache: write at least 4k when committing

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Message-Id: <20210715182634.215340090@linuxfoundation.org>
Date:   Thu, 15 Jul 2021 20:39:57 +0200
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>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 5.12 235/242] dm writecache: write at least 4k when committing

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

commit 867de40c4c23e6d7f89f9ce4272a5d1b1484c122 upstream.

SSDs perform badly with sub-4k writes (because they perfrorm
read-modify-write internally), so make sure writecache writes at least
4k when committing.

Fixes: 991bd8d7bc78 ("dm writecache: commit just one block, not a full page")
Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/md/dm-writecache.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -532,7 +532,11 @@ static void ssd_commit_superblock(struct
 
 	region.bdev = wc->ssd_dev->bdev;
 	region.sector = 0;
-	region.count = wc->block_size >> SECTOR_SHIFT;
+	region.count = max(4096U, wc->block_size) >> SECTOR_SHIFT;
+
+	if (unlikely(region.sector + region.count > wc->metadata_sectors))
+		region.count = wc->metadata_sectors - region.sector;
+
 	region.sector += wc->start_sector;
 
 	req.bi_op = REQ_OP_WRITE;