Порядок 0 соответствует одной странице.
page allocation order
The 'order' of a page allocation is it's logarithm to the base 2, and the size of the allocation is 2order, an integral power-of-2 number of pages. 'Order' ranges from from 0 to MAX_ORDER-1.
The smallest - and most frequent - page allocation is 20 or 1 page.