Re: [PATCH 2/7] mm: Move pt_mm within struct page

[Geert Uytterhoeven]

Hi Matthew,

On Tue, Apr 28, 2020 at 9:44 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> Instead of a per-arch word within struct page, use a formerly reserved
> word.  This word is shared with page->mapping, so it must be cleared
> before being freed as it is checked in free_pages().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

Thanks for your patch!

> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -149,11 +149,8 @@ struct page {
>                                         pgtable_t pmd_huge_pte;
>                                 };
>                         };
> -                       unsigned long _pt_pad_2;        /* mapping */
> -                       union {
> -                               struct mm_struct *pt_mm; /* x86 pgds only */
> -                               atomic_t pt_frag_refcount; /* powerpc */
> -                       };
> +                       struct mm_struct *pt_mm;
> +                       atomic_t pt_frag_refcount; /* powerpc */

So here is now an implicit hole on 64-bit platforms, right?
Do we have any where alignof(long) != 8?

>  #if ALLOC_SPLIT_PTLOCKS
>                         spinlock_t *ptl;
>  #else

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds