linux-kernel - Re: [PATCH] pgtable: do not expose

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Date:   Tue, 21 Nov 2023 15:47:17 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     Vishal Moola <vishal.moola@...il.com>, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Subject: Re: [PATCH] pgtable: do not expose _refcount field via ptdesc

On Tue, Nov 21, 2023 at 01:03:10PM +0100, Alexander Gordeev wrote:
> Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE")
> _refcount field is not used for fragmented page tracking on s390 and
> there is no other code left that accesses this field explicitly.
> 
> Suggested-by: Heiko Carstens <hca@...ux.ibm.com>
> Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
> ---
>  include/linux/mm_types.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 957ce38768b2..0330e0ddca11 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -401,11 +401,10 @@ FOLIO_MATCH(compound_head, _head_2a);
>   * @pmd_huge_pte:     Protected by ptdesc->ptl, used for THPs.
>   * @__page_mapping:   Aliases with page->mapping. Unused for page tables.
>   * @pt_mm:            Used for x86 pgds.
> - * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only.
> + * @pt_frag_refcount: For fragmented page table tracking. Powerpc only.
>   * @_pt_pad_2:        Padding to ensure proper alignment.
>   * @ptl:              Lock for the page table.
>   * @__page_type:      Same as page->page_type. Unused for page tables.
> - * @_refcount:        Same as page refcount. Used for s390 page tables.

I would guess that you need to describe _pt_pad_3 instead here, just
like it is done for the other two pad members.

And most likely you need to add Andrew to "To:" so he doesn't miss
this :)