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    Subject[PATCH 5.10 209/215] dm writecache: write at least 4k when committing
    Date
    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;

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