#ifndef __LINUX_PAGE_EXT_H
  #define __LINUX_PAGE_EXT_H

  #include <linux/types.h>
  #include <linux/stacktrace.h>

  #include <linux/stackdepot.h>

  struct pglist_data;
  struct page_ext_operations {

  	size_t offset;
  	size_t size;

  	bool (*need)(void);
  	void (*init)(void);
  };
  
  #ifdef CONFIG_PAGE_EXTENSION
  
  /*

   * page_ext->flags bits:
   *
   * PAGE_EXT_DEBUG_POISON is set for poisoned pages. This is used to
   * implement generic debug pagealloc feature. The pages are filled with
   * poison patterns and set this flag after free_pages(). The poisoned
   * pages are verified whether the patterns are not corrupted and clear
   * the flag before alloc_pages().
   */
  
  enum page_ext_flags {
  	PAGE_EXT_DEBUG_POISON,		/* Page is poisoned */
  	PAGE_EXT_DEBUG_GUARD,

  	PAGE_EXT_OWNER,

  #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
  	PAGE_EXT_YOUNG,
  	PAGE_EXT_IDLE,
  #endif

  };
  
  /*

   * Page Extension can be considered as an extended mem_map.
   * A page_ext page is associated with every page descriptor. The
   * page_ext helps us add more information about the page.
   * All page_ext are allocated at boot or memory hotplug event,
   * then the page_ext for pfn always exists.
   */
  struct page_ext {
  	unsigned long flags;
  };
  
  extern void pgdat_page_ext_init(struct pglist_data *pgdat);
  
  #ifdef CONFIG_SPARSEMEM
  static inline void page_ext_init_flatmem(void)
  {
  }
  extern void page_ext_init(void);
  #else
  extern void page_ext_init_flatmem(void);
  static inline void page_ext_init(void)
  {
  }
  #endif
  
  struct page_ext *lookup_page_ext(struct page *page);
  
  #else /* !CONFIG_PAGE_EXTENSION */
  struct page_ext;
  
  static inline void pgdat_page_ext_init(struct pglist_data *pgdat)
  {
  }
  
  static inline struct page_ext *lookup_page_ext(struct page *page)
  {
  	return NULL;
  }
  
  static inline void page_ext_init(void)
  {
  }
  
  static inline void page_ext_init_flatmem(void)
  {
  }
  #endif /* CONFIG_PAGE_EXTENSION */
  #endif /* __LINUX_PAGE_EXT_H */