On Tue 05-12-17 18:25:21, Matthew Wilcox wrote:
[...]
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> We don't have to use an entire 'long' for the number of elements in the
> pagevec; we know it's a number between 0 and 14 (now 15). So we can
> store it in a char, and then the bool packs next to it and we still have
> two or six bytes of padding for more elements in the header. That gives
> us space to cram in an extra page.
>
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
> index 5fb6580f7f23..6dc456ac6136 100644
> --- a/include/linux/pagevec.h
> +++ b/include/linux/pagevec.h
> @@ -9,14 +9,14 @@
> #ifndef _LINUX_PAGEVEC_H
> #define _LINUX_PAGEVEC_H
>
> -/* 14 pointers + two long's align the pagevec structure to a power of two */
> -#define PAGEVEC_SIZE 14
> +/* 15 pointers + header align the pagevec structure to a power of two */
> +#define PAGEVEC_SIZE 15
And now you have ruined the ultimate constant of the whole MM :p
But seriously, I have completely missed that pagevec has such a bad
layout.
> struct page;
> struct address_space;
>
> struct pagevec {
> - unsigned long nr;
> + unsigned char nr;
> bool percpu_pvec_drained;
> struct page *pages[PAGEVEC_SIZE];
> };
Anyway the change looks good to me.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
--
Michal Hocko
SUSE Labs
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