[PATCH 5.13 259/266] dm writecache: write at least 4k when committing

Greg Kroah-Hartman
2021-07-15T19:49:59Z

From: Mikulas Patocka <mpatocka@redhat.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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;