dmthin: express low_water in cluster_size not sector size

I noticed that thin-pool sent out "reached low water mark for data
device" event even before thin-pool device was mounted in
generic/347, this is because low water mark was set to a too high
value.

According to kernel thin-provisioning.txt documentation, low water
mark should be expressed in blocks of $cluster_size, not in sectors.

"$low_water_mark is expressed in blocks of size $data_block_size."

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

diff --git a/common/dmthin b/common/dmthin
index 1b5c85698f5210dd6849dcef579ec18da6cdcf45..3cd206a6bc9f645ece3aed9b0cdd0e6d843cbb9a 100644 (file)
--- a/common/dmthin
+++ b/common/dmthin
@@ -91,6 +91,8 @@ _dmthin_init()
        if [ -z "$low_water" ]; then
                low_water=204800        # 100M, in sectors
        fi
+       # low_water is expressed in blocks of size $cluster_size
+       low_water=$((low_water / cluster_size))
 
        # Need to make linear metadata and data devs.  From kernel docs:
        # As a guide, we suggest you calculate the number of bytes to use in the