dm writecache: write at least 4k when committing

stable inclusion
from stable-5.10.51
commit b716ccffbc8dc8f14773d4ae7daadbca6167da2d
bugzilla: 175263 https://gitee.com/openeuler/kernel/issues/I4DT6F

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b716ccffbc8dc8f14773d4ae7daadbca6167da2d

--------------------------------

commit 867de40c 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: 991bd8d7 ("dm writecache: commit just one block, not a full page")
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/md/dm-writecache.c

@@ -532,7 +532,11 @@ static void ssd_commit_superblock(struct dm_writecache *wc)
 
 	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;