#ifndef __ASM_MEMORY_MODEL_H
  #define __ASM_MEMORY_MODEL_H

  #ifndef __ASSEMBLY__
  
  #if defined(CONFIG_FLATMEM)
  
  #ifndef ARCH_PFN_OFFSET
  #define ARCH_PFN_OFFSET		(0UL)
  #endif
  
  #elif defined(CONFIG_DISCONTIGMEM)
  
  #ifndef arch_pfn_to_nid
  #define arch_pfn_to_nid(pfn)	pfn_to_nid(pfn)
  #endif
  
  #ifndef arch_local_page_offset
  #define arch_local_page_offset(pfn, nid)	\
  	((pfn) - NODE_DATA(nid)->node_start_pfn)
  #endif
  
  #endif /* CONFIG_DISCONTIGMEM */

  /*
   * supports 3 memory models.
   */
  #if defined(CONFIG_FLATMEM)

  #define __pfn_to_page(pfn)	(mem_map + ((pfn) - ARCH_PFN_OFFSET))
  #define __page_to_pfn(page)	((unsigned long)((page) - mem_map) + \

  				 ARCH_PFN_OFFSET)
  #elif defined(CONFIG_DISCONTIGMEM)

  #define __pfn_to_page(pfn)			\

  ({	unsigned long __pfn = (pfn);		\

  	unsigned long __nid = arch_pfn_to_nid(__pfn);  \

  	NODE_DATA(__nid)->node_mem_map + arch_local_page_offset(__pfn, __nid);\
  })

  #define __page_to_pfn(pg)						\

  ({	const struct page *__pg = (pg);					\

  	struct pglist_data *__pgdat = NODE_DATA(page_to_nid(__pg));	\
  	(unsigned long)(__pg - __pgdat->node_mem_map) +			\
  	 __pgdat->node_start_pfn;					\

  })

  #elif defined(CONFIG_SPARSEMEM_VMEMMAP)

  /* memmap is virtually contiguous.  */

  #define __pfn_to_page(pfn)	(vmemmap + (pfn))

  #define __page_to_pfn(page)	(unsigned long)((page) - vmemmap)

  #elif defined(CONFIG_SPARSEMEM)
  /*
   * Note: section's mem_map is encorded to reflect its start_pfn.
   * section[i].section_mem_map == mem_map's address - start_pfn;
   */

  #define __page_to_pfn(pg)					\

  ({	const struct page *__pg = (pg);				\

  	int __sec = page_to_section(__pg);			\

  	(unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec)));	\

  })

  #define __pfn_to_page(pfn)				\

  ({	unsigned long __pfn = (pfn);			\
  	struct mem_section *__sec = __pfn_to_section(__pfn);	\
  	__section_mem_map_addr(__sec) + __pfn;		\
  })
  #endif /* CONFIG_FLATMEM/DISCONTIGMEM/SPARSEMEM */

  #define page_to_pfn __page_to_pfn
  #define pfn_to_page __pfn_to_page

  
  #endif /* __ASSEMBLY__ */

  
  #endif