linux-kernel - Re: [PATCH 1/2] LoongArch: Remove zero_page

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Date:   Tue, 5 Sep 2023 18:58:45 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Bibo Mao <maobibo@...ngson.cn>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] LoongArch: Remove zero_page_mask symbol

Hi, Bibo,

On Tue, Sep 5, 2023 at 4:01 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> On LoongArch system, there is only one page for zero page, and
> there is no COLOR_ZERO_PAGE, so zero_page_mask is useless and
> macro __HAVE_COLOR_ZERO_PAGE is not necessary. This patch removes
> zero_page_mask and macro __HAVE_COLOR_ZERO_PAGE.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/loongarch/include/asm/pgtable.h | 4 +---
>  arch/loongarch/mm/init.c             | 9 +--------
>  2 files changed, 2 insertions(+), 11 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index 06963a172319..342c5f9c25d2 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -71,11 +71,9 @@ struct vm_area_struct;
>   */
>
>  extern unsigned long empty_zero_page;
> -extern unsigned long zero_page_mask;
>
>  #define ZERO_PAGE(vaddr) \
> -       (virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask))))
> -#define __HAVE_COLOR_ZERO_PAGE
> +       (virt_to_page((void *)(empty_zero_page)))
>
>  /*
>   * TLB refill handlers may also map the vmalloc area into xkvrange.
> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> index 3b7d8129570b..8ec668f97b00 100644
> --- a/arch/loongarch/mm/init.c
> +++ b/arch/loongarch/mm/init.c
> @@ -35,14 +35,8 @@
>  #include <asm/pgalloc.h>
>  #include <asm/tlb.h>
>
> -/*
> - * We have up to 8 empty zeroed pages so we can map one of the right colour
> - * when needed.         Since page is never written to after the initialization we
> - * don't have to care about aliases on other CPUs.
> - */
> -unsigned long empty_zero_page, zero_page_mask;
> +unsigned long empty_zero_page;
>  EXPORT_SYMBOL(empty_zero_page);
> -EXPORT_SYMBOL(zero_page_mask);
>
>  void setup_zero_pages(void)
>  {
> @@ -60,7 +54,6 @@ void setup_zero_pages(void)
>         for (i = 0; i < (1 << order); i++, page++)
>                 mark_page_reserved(page);
>
> -       zero_page_mask = ((PAGE_SIZE << order) - 1) & PAGE_MASK;
In my opinion it is better to combine two patches to one. Because this
patch can only work *accidently* when 'order' is zero.

Huacai
>  }
>
>  void copy_user_highpage(struct page *to, struct page *from,
> --
> 2.27.0
>
>