[PATCH v1] Docs/mm: Fix a mistakes for pfn in page_tables.rst

[PATCH v1] Docs/mm: Fix a mistakes for pfn in page_tables.rst

[Pengyu Zhang]

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@gmail.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
-- 
2.25.1

Re: [PATCH v1] Docs/mm: Fix a mistakes for pfn in page_tables.rst

[Mike Rapoport]

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@gmail.com>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.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.

Re: [PATCH v1] Docs/mm: Fix a mistakes for pfn in page_tables.rst

[Zenghui Yu]

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@gmail.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@linux.dev>