Man page 9 : alloc_contig_range

alloc_contig_range - - tries to allocate given range of pages

int alloc_contig_range(unsigned long  start , unsigned long  end , unsigned  migratetype );

start
    start PFN to allocate

end
    one-past-the-last PFN to allocate

migratetype
    migratetype of the underlaying pageblocks (either #MIGRATE_MOVABLE or #MIGRATE_CMA). All pageblocks in range must have the same migratetype and it must be either of the two.

The PFN range does not have to be pageblock or MAX_ORDER_NR_PAGES aligned, however itAqs the callerAqs responsibility to guarantee that we are the only thread that changes migrate type of pageblocks the pages fall in.

The PFN range must belong to a single zone.

Returns zero on success or negative error code. On success all pages which PFN is in [start, end) are allocated for the caller and need to be freed with free_contig_range.