Re: [PATCH v11 01/25] mm/gup: factor out duplicate code from four routines

Kirill A. Shutemov
2019-12-18T15:52:18Z

On Mon, Dec 16, 2019 at 02:25:13PM -0800, John Hubbard wrote:
> +static void put_compound_head(struct page *page, int refs)
> +{
> + /* Do a get_page() first, in case refs == page->_refcount */
> + get_page(page);
> + page_ref_sub(page, refs);
> + put_page(page);
> +}

It's not terribly efficient. Maybe something like:

VM_BUG_ON_PAGE(page_ref_count(page) < ref, page);
if (refs > 2)
page_ref_sub(page, refs - 1);
put_page(page);

?

--
Kirill A. Shutemov