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

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Message-ID: <988d7c7d-dedd-4ceb-ad8a-9a9962b7bb0c@linux.dev>
Date: Wed, 9 Oct 2024 00:25:54 +0800
From: Zenghui Yu <zenghui.yu@...ux.dev>
To: Pengyu Zhang <zpenya1314@...il.com>
Cc: corbet@....net, rppt@...nel.org, 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

s/mistakes/mistake/ in the Subject line.

On 2024/10/9 00:10, Pengyu Zhang wrote:
> The documentation incorrectly calculate the pfn value as 0x3fffff,
> which should be 0x3ffff instead.It is obtained by right-shifting
                                  ^
Add a space.

> 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>
> ---
>  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

Reviewed-by: Zenghui Yu <zenghui.yu@...ux.dev>