On Mon 17-08-15 18:09:04, Kirill A. Shutemov wrote:
> The patch halves space occupied by compound_dtor and compound_order in
> struct page.
>
> For compound_order, it's trivial long -> int/short conversion.
>
> For get_compound_page_dtor(), we now use hardcoded table for destructor
> lookup and store its index in the struct page instead of direct pointer
> to destructor. It shouldn't be a big trouble to maintain the table: we
> have only two destructor and NULL currently.
>
> This patch free up one word in tail pages for reuse. This is preparation
> for the next patch.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxxx>
[...]
> @@ -145,8 +143,13 @@ struct page {
> */
> /* First tail page of compound page */
> struct {
> - compound_page_dtor *compound_dtor;
> - unsigned long compound_order;
> +#ifdef CONFIG_64BIT
> + unsigned int compound_dtor;
> + unsigned int compound_order;
> +#else
> + unsigned short int compound_dtor;
> + unsigned short int compound_order;
> +#endif
> };
Why do we need this ifdef? We can go with short for both 32b and 64b
AFAICS. We do not use compound_order for anything else than the order,
right?
While I am looking at this, it seems we are jugling with type for order
quite a lot - int, unsing int and even unsigned long.
--
Michal Hocko
SUSE Labs
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