hi,

> > > Is is it simply that the read will block indefinitely waiting for the
> > > write to happen, with no way to cause the delayed-write queue to be
> > > flushed?
> > 
> > yes.
> 
> Why would these reads be generated?  If the write has not completed, is
> it not the case that the page must still be dirty, and should thus still
> be in the cache?

because the page is marked as PG_BUSY during delayed write,
VOP_GETPAGES will wait on it.  we have no way to hurry
the i/o in this case.

maybe distinguishing PG_BUSY-for-read and PG_BUSY-for-write can be
an alternative solution?

YAMAMOTO Takashi