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    Subject[PATCH 3.12 092/170] dm thin: update discard_granularity to reflect the thin-pool blocksize
    Date
    From: Lukas Czerner <lczerner@redhat.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit 09869de57ed2728ae3c619803932a86cb0e2c4f8 upstream.

    DM thinp already checks whether the discard_granularity of the data
    device is a factor of the thin-pool block size. But when using the
    dm-thin-pool's discard passdown support, DM thinp was not selecting the
    max of the underlying data device's discard_granularity and the
    thin-pool's block size.

    Update set_discard_limits() to set discard_granularity to the max of
    these values. This enables blkdev_issue_discard() to properly align the
    discards that are sent to the DM thin device on a full block boundary.
    As such each discard will now cover an entire DM thin-pool block and the
    block will be reclaimed.

    Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
    Signed-off-by: Lukas Czerner <lczerner@redhat.com>
    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    drivers/md/dm-thin.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
    index e4cc196634c1..f8c36d30eca8 100644
    --- a/drivers/md/dm-thin.c
    +++ b/drivers/md/dm-thin.c
    @@ -2695,7 +2695,8 @@ static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits)
    */
    if (pt->adjusted_pf.discard_passdown) {
    data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
    - limits->discard_granularity = data_limits->discard_granularity;
    + limits->discard_granularity = max(data_limits->discard_granularity,
    + pool->sectors_per_block << SECTOR_SHIFT);
    } else
    limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
    }
    --
    2.0.0


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