Re: [PATCHv12 26/37] mm: rework mapcount accounting to enable 4k mapping of THPs

From: Naoya Horiguchi
Date: Fri Oct 30 2015 - 04:34:40 EST

On Thu, Oct 29, 2015 at 11:50:47PM +0200, Kirill A. Shutemov wrote:
> Okay, the problem is that the page was freed under stable_page_flags().
> Is the code performance sensitive? Can we get reference to the page before
> touching it? If not, we can rewrite the helper like this:
> static inline int PageDoubleMap(struct page *page)
> {
> return PageHead(page) && test_bit(PG_double_map, &page[1].flags);
> }
> Just dropping the check would be wrong, I think, as we access the next
> page.

I don't think this interface is performance sensitive, but hopefully the
impact on other workload is minimum. So I like the above rewritten one.

Naoya Horiguchi--
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