On 28 Jan 2021, at 2:03, Matthew Wilcox (Oracle) wrote:
> If we know we have a folio, we can call get_folio() instead of get_page()
> and save the overhead of calling compound_head().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> include/linux/mm.h | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 873d649107ba..d71c5776b571 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1192,18 +1192,19 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
> }
>
> /* 127: arbitrary random number, small enough to assemble well */
> -#define page_ref_zero_or_close_to_overflow(page) \
> - ((unsigned int) page_ref_count(page) + 127u <= 127u)
> +#define folio_ref_zero_or_close_to_overflow(folio) \
> + ((unsigned int) page_ref_count(&folio->page) + 127u <= 127u)
> +
> +static inline void get_folio(struct folio *folio)
> +{
> + /* Getting a page requires an already elevated page->_refcount. */
> + VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
> + page_ref_inc(&folio->page);
> +}
>
> static inline void get_page(struct page *page)
> {
> - page = compound_head(page);
> - /*
> - * Getting a normal page or the head of a compound page
> - * requires to already have an elevated page->_refcount.
> - */
> - VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
> - page_ref_inc(page);
> + get_folio(page_folio(page));
> }
>
> bool __must_check try_grab_page(struct page *page, unsigned int flags);
> --
> 2.29.2
LGTM.
Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
—
Best Regards,
Yan Zi
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