Julian Elischer wrote:
>
> no.. it has to do with the fact that it would be unwise
> to make a cluster > 1 page size since we have no guarantee that
> all drivers could handle breaking up a DMA if a cluster spanned 2
> physical address ranges. (they can handle a chain of discontinuous
> mbufs but may assume that a single mbuf will have physically
> contiguous data. Now since we cannot span a page boundary,
> we should fit in exacly to get as much room as possible
> and since (pagesize/3) is too small, the next possibility is (pagesize/2).
FWIW: the way clusters work quarantees contiguity, based on
the zone allocator being backed by contiguous regions in
single pages.
This is what Julian said, but it's less verbose... 8-).
-- Terry
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