lvs -a
This should show the meta data volume to be something like
thinpool_tmeta
Here it is tp0_tmeta. Now you can extend the tp0_tmeta as like any other logical volume:[root@lvetest1 ~]# lvs -a
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
[lvol0_pmspare] vg0 ewi------- 64.00m
tp0 vg0 twi-aotz-- 64.00g 0.81 0.87
[tp0_tdata] vg0 Twi-ao---- 64.00g
[tp0_tmeta] vg0 ewi-ao---- 64.00m
lvextend -L+128M /dev/vg0/tp0_tmeta
Done!