dtrace: two buffers for ring and fill policies?

I've just noticed that DTrace allocates two per-CPU principal buffers even when 
a bufpolicy of ring or fill is used.
I believe that the second buffer is never used in those cases.

This is the code:
                 if (flags & DTRACEBUF_NOSWITCH)
                         continue;

                 if ((buf->dtb_xamot = kmem_zalloc(size,
                     KM_NOSLEEP | KM_NORMALPRI)) == NULL)
                         goto err;

As far as I can see,  DTRACEBUF_NOSWITCH is not implied by DTRACEBUF_RING or 
DTRACEBUF_FILL.
Maybe it should be?

-- 
Andriy Gapon