* a smaller number of blocks (producing a smaller extent), with
* this smaller number of blocks consisting of the requested
* number of blocks rounded down to the next smaller power of 2
* number (i.e. 16 -> 8). we'll continue to round down and
* retry the allocation until the number of blocks to allocate
* is smaller than the number of blocks per page.
* a smaller number of blocks (producing a smaller extent), with
* this smaller number of blocks consisting of the requested
* number of blocks rounded down to the next smaller power of 2
* number (i.e. 16 -> 8). we'll continue to round down and
* retry the allocation until the number of blocks to allocate
* is smaller than the number of blocks per page.