[PATCH 0/3] simplify the writeback code

[Christoph Hellwig]

The writeback path has a lot of code that's been dead for a while.  We're
never asked to release dirty and thus delayed allocated or unwritten pages
from ->releasepage, and since the introduction of ->page_mkwrite we also
don't have to deal with dirty but unmapped buffers in ->writepage.  But
there's a case masquerading as such, which needs to be fixed by a 1.5 years
old patch from Eric first.  That patch also happens to fix xfstests 194.