On Mon, 2012-09-10 at 16:13 +0300, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>
> H. Peter Anvin doesn't like huge zero page which sticks in memory forever
> after the first allocation. Here's implementation of lockless refcounting
> for huge zero page.
>
...
> +static unsigned long get_huge_zero_page(void)
> +{
> + struct page *zero_page;
> +retry:
> + if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
> + return ACCESS_ONCE(huge_zero_pfn);
> +
> + zero_page = alloc_pages(GFP_TRANSHUGE | __GFP_ZERO, HPAGE_PMD_ORDER);
> + if (!zero_page)
> + return 0;
> + if (cmpxchg(&huge_zero_pfn, 0, page_to_pfn(zero_page))) {
> + __free_page(zero_page);
> + goto retry;
> + }
This might break if preemption can happen here ?
The second thread might loop forever because huge_zero_refcount is 0,
and huge_zero_pfn not zero.
If preemption already disabled, a comment would be nice.
> +
> + /* We take additional reference here. It will be put back by shinker */
typo : shrinker
> + atomic_set(&huge_zero_refcount, 2);
> + return ACCESS_ONCE(huge_zero_pfn);
> +}
> +
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