linux-kernel - Re: [PATCH v2 2/3] x86/mm/doc: Clean up the memory region layout descriptions

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Date:   Tue, 2 Oct 2018 11:14:12 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-doc@...r.kernel.org, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com, thgarnie@...gle.com,
        corbet@....net
Subject: Re: [PATCH v2 2/3] x86/mm/doc: Clean up the memory region layout
 descriptions


* Baoquan He <bhe@...hat.com> wrote:

> In Documentation/x86/x86_64/mm.txt, the style of descritions about
> memory region layout is a little confusing:
> 
>  - mix size in TB with 'bits'
>  - sometimes mention a size in the description and sometimes not
>  - sometimes list holes by address, sometimes only as an 'unused hole' line
> 
> So fix them to make them in consistent style.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  Documentation/x86/x86_64/mm.txt | 76 ++++++++++++++++++++---------------------
>  1 file changed, 38 insertions(+), 38 deletions(-)
> 
> diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
> index 5432a96d31ff..fc1da95e629d 100644
> --- a/Documentation/x86/x86_64/mm.txt
> +++ b/Documentation/x86/x86_64/mm.txt
> @@ -1,52 +1,52 @@
>  
>  Virtual memory map with 4 level page tables:
>  
> -0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
> -hole caused by [47:63] sign extension
> -ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
> -ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
> -ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
> -ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
> -ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
> -ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
> -... unused hole ...
> -ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB)
> -... unused hole ...
> +0000000000000000 - 00007fffffffffff (=47 bits, 128 TB) user space, different per mm
> +				    hole caused by [47:63] sign extension
> +ffff800000000000 - ffff87ffffffffff (=43 bits, 8 TB) guard hole, reserved for hypervisor
> +ffff880000000000 - ffffc7ffffffffff (=46 bits, 64 TB) direct mapping of all phys. memory (page_offset_base)
> +ffffc80000000000 - ffffc8ffffffffff (=40 bits, 1 TB) unused hole
> +ffffc90000000000 - ffffe8ffffffffff (=45 bits, 32 TB) vmalloc/ioremap space (vmalloc_base)
> +ffffe90000000000 - ffffe9ffffffffff (=40 bits, 1 TB) unused hole
> +ffffea0000000000 - ffffeaffffffffff (=40 bits, 1 TB) virtual memory map (vmemmap_base)
> +ffffeb0000000000 - ffffebffffffffff (=40 bits, 1 TB) unused hole
> +ffffec0000000000 - fffffbffffffffff (=44 bits, 16 TB) kasan shadow memory
> +fffffc0000000000 - fffffdffffffffff (=41 bits, 2 TB) unused hole
>  				    vaddr_end for KASLR
> -fffffe0000000000 - fffffe7fffffffff (=39 bits) cpu_entry_area mapping
> -fffffe8000000000 - fffffeffffffffff (=39 bits) LDT remap for PTI
> -ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
> -... unused hole ...
> -ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
> -... unused hole ...
> -ffffffff80000000 - ffffffff9fffffff (=512 MB)  kernel text mapping, from phys 0
> -ffffffffa0000000 - fffffffffeffffff (1520 MB) module mapping space
> +fffffe0000000000 - fffffe7fffffffff (=39 bits, 512 GB) cpu_entry_area mapping
> +fffffe8000000000 - fffffeffffffffff (=39 bits, 512 GB) LDT remap for PTI
> +ffffff0000000000 - ffffff7fffffffff (=39 bits, 512 GB) %esp fixup stacks
> +ffffff8000000000 - fffffffeefffffff (~39 bits, ~507 GB) unused hole
> +ffffffef00000000 - fffffffeffffffff (=36 bits, 64 GB) EFI region mapping space
> +ffffffff00000000 - ffffffff7fffffff (=31 bits, 2 GB) unused hole
> +ffffffff80000000 - ffffffff9fffffff (=29 bits, 512 MB)  kernel text mapping, from phys 0
> +ffffffffa0000000 - fffffffffeffffff (~31 bits, 1520 MB) module mapping space
>  [fixmap start]   - ffffffffff5fffff kernel-internal fixmap range
>  ffffffffff600000 - ffffffffff600fff (=4 kB) legacy vsyscall ABI
>  ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole

Looks mostly good now, but could you please make the right side align vertically as well, like 
I did in the examples I provided previously?

There's zero reason for it to look this disorganized:

> +ffffff8000000000 - fffffffeefffffff (~39 bits, ~507 GB) unused hole
> +ffffffef00000000 - fffffffeffffffff (=36 bits, 64 GB) EFI region mapping space
> +ffffffff00000000 - ffffffff7fffffff (=31 bits, 2 GB) unused hole
> +ffffffff80000000 - ffffffff9fffffff (=29 bits, 512 MB)  kernel text mapping, from phys 0

I.e. can we do something like:

> +ffffff8000000000 - fffffffeefffffff (~39 bits, ~507 GB) unused hole
> +ffffffef00000000 - fffffffeffffffff (=36 bits,   64 GB) EFI region mapping space
> +ffffffff00000000 - ffffffff7fffffff (=31 bits,    2 GB) unused hole
> +ffffffff80000000 - ffffffff9fffffff (=29 bits,  512 MB) kernel text mapping, from phys 0

?

That not only makes it more readable, but makes typos like the whitespace noise double space in 
the last line more obvious.

Thanks,

	Ingo