skip blocks that are too big by a factor of two or greater. This
avoids some cases of extremely inefficient memory use that can occur
when large (e.g. 64k) blocks on the free list get used when allocating
a 4k chunk of 64-byte fragments. Because fragments have their own
free list, the 60k difference got lost forever every time.
allocation function. With this patch, it prevents continous growth of
the devbuf memory pool.
Tested with ssh <host> dd of=/dev/null < /dev/zero and vmstat -m | grep devbuf
go looking for free fragments won't match. Since we never free this, we
can "throw away" the tag. This is very dirty, and needs to be reimplemented
properly, but fixes performance problems with uhci.
Also assert that when we overlay a structure on some space, that the
space is large enough for the structure.
