linux-kernel - Re: [RFC 0/4] arm64/mm: Clean up pte

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Message-ID: <ZKvqjrpyLZVB3R2z@FVFF77S0Q05N>
Date:   Mon, 10 Jul 2023 12:25:02 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [RFC 0/4] arm64/mm: Clean up pte_dirty() state management

On Fri, Jul 07, 2023 at 11:03:27AM +0530, Anshuman Khandual wrote:
> These pte_dirty() changes make things explicitly clear, while improving the
> code readability. This optimizes HW dirty state transfer into SW dirty bit.
> This also adds a new arm64 documentation explaining overall pte dirty state
> management in detail. This series applies on the latest mainline kernel.

TBH, I think this is all swings and roundabouts, and I'm not sure this is
worthwhile. I appreciate that as-is some people find this confusing, but I
don't think the end result of this series is actually better, and it adds more
code/documentation to maintain.

In particular, I don't think that we should add Documentation/ files for this,
as it's very likely that won't be updated together with the code, and I think
it's more of a maintenance burden than a help. If we want some introductory
text to explain how the HW/SW dirty bits work, I think that should be a comment
block in <asm/pgtable.h>, clearly associated with the code.

Overall, I'd prefer to leave the code as-is.

Thanks,
Mark.

> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> 
> Anshuman Khandual (4):
>   arm64/mm: Add SW and HW dirty state helpers
>   arm64/mm: Call pte_sw_mkdirty() while preserving the HW dirty state
>   arm64/mm: Add pte_preserve_hw_dirty()
>   docs: arm64: Add help document for pte dirty state management
> 
>  Documentation/arch/arm64/index.rst     |  1 +
>  Documentation/arch/arm64/pte-dirty.rst | 95 ++++++++++++++++++++++++++
>  arch/arm64/include/asm/pgtable.h       | 66 ++++++++++++++----
>  3 files changed, 147 insertions(+), 15 deletions(-)
>  create mode 100644 Documentation/arch/arm64/pte-dirty.rst
> 
> -- 
> 2.30.2
>