linux-kernel - Re: [PATCH v1] Docs/mm: Fix a mistakes for pfn in page

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Message-ID: <ZwVbSSBf2NM_yq1H@kernel.org>
Date: Tue, 8 Oct 2024 19:18:17 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Pengyu Zhang <zpenya1314@...il.com>
Cc: corbet@....net, linus.walleij@...aro.org, fmdefrancesco@...il.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] Docs/mm: Fix a mistakes for pfn in page_tables.rst

On Wed, Oct 09, 2024 at 12:10:50AM +0800, Pengyu Zhang wrote:
> The documentation incorrectly calculate the pfn value as 0x3fffff,
> which should be 0x3ffff instead.It is obtained by right-shifting
> 0xffffc000 by 14 bits.
> 
> This patch corrects the value to prevent any potential confusion
> for developers referencing this document.
> 
> Signed-off-by: Pengyu Zhang <zpenya1314@...il.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  Documentation/mm/page_tables.rst | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Documentation/mm/page_tables.rst b/Documentation/mm/page_tables.rst
> index be47b192a596..e7c69cc32493 100644
> --- a/Documentation/mm/page_tables.rst
> +++ b/Documentation/mm/page_tables.rst
> @@ -29,7 +29,7 @@ address.
>  With a page granularity of 4KB and a address range of 32 bits, pfn 0 is at
>  address 0x00000000, pfn 1 is at address 0x00001000, pfn 2 is at 0x00002000
>  and so on until we reach pfn 0xfffff at 0xfffff000. With 16KB pages pfs are
> -at 0x00004000, 0x00008000 ... 0xffffc000 and pfn goes from 0 to 0x3fffff.
> +at 0x00004000, 0x00008000 ... 0xffffc000 and pfn goes from 0 to 0x3ffff.
>  
>  As you can see, with 4KB pages the page base address uses bits 12-31 of the
>  address, and this is why `PAGE_SHIFT` in this case is defined as 12 and
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.