When one uses XFS on thinp, there are a number of issues that arise: One is just that the 'df' utility doesn't return relevant information about the space actually available to the filesystem. Two, there may not be sufficient coordination between the two layers when running low on space in the thin pool. Three, it's not clear (at least to me) the degree which being on thinp affects XFS performance characteristics, and how efficient XFS is in resisting fragmentation and inefficient usage of thinp blocks. It would be good to analyze and possibly improve XFS's behavior in this area.
This bug appears to have been reported against 'rawhide' during the Fedora 26 development cycle. Changing version to '26'.
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