linux-kernel - Re: [PATCH v5 00/12] mm: establish const-correctness for pointer parameters

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Message-ID: <20250901-ungut-geerntet-51b9f03284be@brauner>
Date: Mon, 1 Sep 2025 15:44:51 +0200
From: Christian Brauner <brauner@...nel.org>
To: Max Kellermann <max.kellermann@...os.com>
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Subject: Re: [PATCH v5 00/12] mm: establish const-correctness for pointer
 parameters

On Mon, Sep 01, 2025 at 02:30:16PM +0200, Max Kellermann wrote:
> For improved const-correctness.
> 
> This patch series systematically adds const qualifiers to pointer
> parameters throughout the memory management subsystem, establishing a
> foundation for improved const-correctness across the entire Linux
> kernel.
> 
> Const-correctness provides multiple benefits:
> 
> 1. Type Safety: The compiler enforces that functions marked as taking
>    const parameters cannot accidentally modify the data, catching
>    potential bugs at compile time rather than runtime.
> 
> 2. Compiler Optimizations: When the compiler knows data won't be
>    modified, it can generate more efficient code through better
>    register allocation, code motion, and aliasing analysis.
> 
> 3. API Documentation: Const qualifiers serve as self-documenting code,
>    making it immediately clear to developers which functions are
>    read-only operations versus those that modify state.
> 
> 4. Maintenance Safety: Future modifications to const-correct code are
>    less likely to introduce subtle bugs, as the compiler will reject
>    attempts to modify data that should remain unchanged.
> 
> The memory management subsystem is a fundamental building block of the
> kernel.  Most higher-level kernel subsystems (filesystems, drivers,
> networking) depend on mm interfaces.  By establishing
> const-correctness at this foundational level:
> 
> 1. Enables Propagation: Higher-level subsystems can adopt
>    const-correctness in their own interfaces.  Without const-correct
>    mm functions, filesystems cannot mark their own parameters const
>    when they need to call mm functions.
> 
> 2. Maximum Impact: Changes to core mm APIs benefit the entire kernel, as
>    these functions are called from virtually every subsystem.
> 
> 3. Prevents Impedance Mismatch: Without const-correctness in mm, other
>    subsystems must either cast away const (dangerous) or avoid using
>    const altogether (missing optimization opportunities).
> 
> Each patch focuses on a specific header or subsystem component to ease review
> and bisection.
> 
> This work was initially posted as a single large patch:
>  https://lore.kernel.org/lkml/20250827192233.447920-1-max.kellermann@ionos.com/
> 
> Following feedback from Lorenzo Stoakes and David Hildenbrand, it has been
> split into focused, reviewable chunks. The approach was validated with a
> smaller patch that received agreement:
>  https://lore.kernel.org/lkml/20250828130311.772993-1-max.kellermann@ionos.com/
> 
> Signed-off-by: Max Kellermann <max.kellermann@...os.com>

Seems fine,
Reviewed-by: Christian Brauner <brauner@...nel.org>