strange PAGE_ALLOC_COSTLY_ORDER usage in xgbe_map_rx_buffer

[Michal Hocko]

Hi Tom,
I have stumbled over the following construct in xgbe_map_rx_buffer
        order = max_t(int, PAGE_ALLOC_COSTLY_ORDER - 1, 0);
which looks quite suspicious. Why does it PAGE_ALLOC_COSTLY_ORDER - 1?
And why do you depend on PAGE_ALLOC_COSTLY_ORDER at all?

Thanks!
-- 
Michal Hocko
SUSE Labs