拆分与合并连续物理页

822		if (page_is_guard(buddy))823			clear_page_guard(zone, buddy, order);824		else825			__del_page_from_free_list(buddy, zone, order, buddy_mt);826827		if (unlikely(buddy_mt != migratetype)) {828			/*829			 * Match buddy type. This ensures that an830			 * expand() down the line puts the sub-blocks831			 * on the right freelists.832			 */833			set_pageblock_migratetype(buddy, migratetype);834		}835836		combined_pfn = buddy_pfn & pfn;837		page = page + (combined_pfn - pfn);838		pfn = combined_pfn;839		order++;840	}841842done_merging:843	set_buddy_order(page, order);