linux-kernel - Re: [PATCH v2] LoongArch: Code cleanup with zero page

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Date:   Thu, 7 Sep 2023 09:37:22 +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 v2] LoongArch: Code cleanup with zero page

Queued for loongarch-next with the old title "LoongArch: Use static
defined zero page rather than allocated" since it is more clear,
thanks.

Huacai

On Thu, Sep 7, 2023 at 9:22 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> Like other popular architectures, zero page is defined in kernel
> BSS data segment, rather than dynamically allocated. It is simpler.
> Also this patch removes macro __HAVE_COLOR_ZERO_PAGE and variable
> zero_page_mask since there is only one page for zeo_page usage.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
> Changes in v2:
>  1. Combine two simple patches into one
>  2. Refine implementation about macro ZERO_PAGE(vaddr)
>
> ---
>  arch/loongarch/include/asm/mmzone.h  |  2 --
>  arch/loongarch/include/asm/pgtable.h |  9 ++-------
>  arch/loongarch/kernel/numa.c         |  1 -
>  arch/loongarch/mm/init.c             | 28 +---------------------------
>  4 files changed, 3 insertions(+), 37 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/mmzone.h b/arch/loongarch/include/asm/mmzone.h
> index fe67d0b4b33d..2b9a90727e19 100644
> --- a/arch/loongarch/include/asm/mmzone.h
> +++ b/arch/loongarch/include/asm/mmzone.h
> @@ -13,6 +13,4 @@ extern struct pglist_data *node_data[];
>
>  #define NODE_DATA(nid) (node_data[(nid)])
>
> -extern void setup_zero_pages(void);
> -
>  #endif /* _ASM_MMZONE_H_ */
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index 06963a172319..189156d8435c 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -69,13 +69,8 @@ struct vm_area_struct;
>   * ZERO_PAGE is a global shared page that is always zero; used
>   * for zero-mapped memory areas etc..
>   */
> -
> -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
> +extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
> +#define ZERO_PAGE(vaddr)       (virt_to_page(empty_zero_page))
>
>  /*
>   * TLB refill handlers may also map the vmalloc area into xkvrange.
> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
> index 708665895b47..6f464d49f0c2 100644
> --- a/arch/loongarch/kernel/numa.c
> +++ b/arch/loongarch/kernel/numa.c
> @@ -470,7 +470,6 @@ void __init mem_init(void)
>  {
>         high_memory = (void *) __va(get_num_physpages() << PAGE_SHIFT);
>         memblock_free_all();
> -       setup_zero_pages();     /* This comes from node 0 */
>  }
>
>  int pcibus_to_node(struct pci_bus *bus)
> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> index 3b7d8129570b..628ebe42b519 100644
> --- a/arch/loongarch/mm/init.c
> +++ b/arch/loongarch/mm/init.c
> @@ -35,33 +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[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
>  EXPORT_SYMBOL(empty_zero_page);
> -EXPORT_SYMBOL(zero_page_mask);
> -
> -void setup_zero_pages(void)
> -{
> -       unsigned int order, i;
> -       struct page *page;
> -
> -       order = 0;
> -
> -       empty_zero_page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> -       if (!empty_zero_page)
> -               panic("Oh boy, that early out of memory?");
> -
> -       page = virt_to_page((void *)empty_zero_page);
> -       split_page(page, order);
> -       for (i = 0; i < (1 << order); i++, page++)
> -               mark_page_reserved(page);
> -
> -       zero_page_mask = ((PAGE_SIZE << order) - 1) & PAGE_MASK;
> -}
>
>  void copy_user_highpage(struct page *to, struct page *from,
>         unsigned long vaddr, struct vm_area_struct *vma)
> @@ -106,7 +81,6 @@ void __init mem_init(void)
>         high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
>
>         memblock_free_all();
> -       setup_zero_pages();     /* Setup zeroed pages.  */
>  }
>  #endif /* !CONFIG_NUMA */
>
> --
> 2.27.0
>
>