最近需要修改linux内核代码中ksm部分，所以记录下遇到的一些重要函数，方便以后查阅与理解。

重要函数

PageTransHuge

函数原型：static inline int PageTransHuge(struct page *page)

函数功能： returns true for both transparent huge and hugetlbfs pages, but not normal pages.

PageTransCompound

函数原型： static inline int PageTransCompound(struct page *page)

函数功能： 如果page是透明大页，则返回true

page_trans_compound_anon

函数原型： static struct page * page_trans_compound_anon(struct page *page)

函数代码：

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static struct page *page_trans_compound_anon(struct page *page)
{
	if (PageTransCompound(page)) {
		struct page *head = compound_head(page);
		/*
		 * head may actually be splitted and freed from under
		 * us but it's ok here.
		 */
		if (PageAnon(head))
			return head;
	}
	return NULL;
}

函数功能： *head等于compound_head(page)，如果PageAnon(head)则返回head，否则返回NULL

split_huge_page

函数原型： static inline int split_huge_page(struct page *page)

函数功能： splits huge page into normal pages；
Returns 0 if the hugepage is split successfully；
Returns -EBUSY if the page is pinned or if anon_vma disappeared from under us.

page_trans_compound_anon_split

函数原型： static int page_trans_compound_anon_split(struct page *page)

函数代码：

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static int page_trans_compound_anon_split(struct page *page)
{
	int ret = 0;
	struct page *transhuge_head = page_trans_compound_anon(page);
	if (transhuge_head) {
		/* Get the reference on the head to split it. */
		if (get_page_unless_zero(transhuge_head)) {
			/*
			 * Recheck we got the reference while the head
			 * was still anonymous.
			 */
			if (PageAnon(transhuge_head))
				ret = split_huge_page(transhuge_head);
			else
				/*
				 * Retry later if split_huge_page run
				 * from under us.
				 */
				ret = 1;
			put_page(transhuge_head);
		} else
			/* Retry later if split_huge_page run from under us. */
			ret = 1;
	}
	return ret;
}

函数功能： 拆分复合透明匿名页，若拆分成功返回0,否则返回非0

参考资料：

  1. 复合页

  2. ksm源码