Messages in this thread | | | Subject | Re: [PATCH v2 10/10] thp: implement refcounting for huge zero page | From | Eric Dumazet <> | Date | Mon, 10 Sep 2012 16:02:39 +0200 |
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On Mon, 2012-09-10 at 16:13 +0300, Kirill A. Shutemov wrote: > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > > 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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