^^&&^^

Edit File: page_ref.h

#ifndef _LINUX_PAGE_REF_H
#define _LINUX_PAGE_REF_H

#include <linux/atomic.h>
#include <linux/mm_types.h>
#include <linux/page-flags.h>

static inline struct page *compound_head_by_tail(struct page *tail)
{
	struct page *head = tail->first_page;

/*
	 * page->first_page may be a dangling pointer to an old
	 * compound page, so recheck that it is still a tail
	 * page before returning.
	 */
	smp_rmb();
	if (likely(PageTail(tail)))
		return head;
	return tail;
}

static inline struct page *compound_head(struct page *page)
{
	if (unlikely(PageTail(page)))
		return compound_head_by_tail(page);
	return page;
}

static inline int page_ref_count(struct page *page)
{
	return atomic_read(&page->_count);
}

static inline int page_count(struct page *page)
{
	return atomic_read(&compound_head(page)->_count);
}

static inline void set_page_count(struct page *page, int v)
{
	atomic_set(&page->_count, v);
}

/*
 * Setup the page count before being freed into the page allocator for
 * the first time (boot or memory hotplug)
 */
static inline void init_page_count(struct page *page)
{
	set_page_count(page, 1);
}

static inline void page_ref_add(struct page *page, int nr)
{
	atomic_add(nr, &page->_count);
}

static inline void page_ref_sub(struct page *page, int nr)
{
	atomic_sub(nr, &page->_count);
}

static inline void page_ref_inc(struct page *page)
{
	atomic_inc(&page->_count);
}

static inline void page_ref_dec(struct page *page)
{
	atomic_dec(&page->_count);
}

static inline int page_ref_sub_and_test(struct page *page, int nr)
{
	return atomic_sub_and_test(nr, &page->_count);
}

static inline int page_ref_dec_and_test(struct page *page)
{
	return atomic_dec_and_test(&page->_count);
}

static inline int page_ref_dec_return(struct page *page)
{
	return atomic_dec_return(&page->_count);
}

static inline int page_ref_add_unless(struct page *page, int nr, int u)
{
	return atomic_add_unless(&page->_count, nr, u);
}

static inline int page_ref_freeze(struct page *page, int count)
{
	return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
}

static inline void page_ref_unfreeze(struct page *page, int count)
{
	VM_BUG_ON_PAGE(page_count(page) != 0, page);
	VM_BUG_ON(count == 0);

atomic_set(&page->_count, count);
}

#endif