linux-kernel - Re: [PATCH v3 27/34] mm: pagewalk: Add 'depth' parameter to pte

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Date:   Wed, 27 Feb 2019 09:38:48 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Steven Price <steven.price@....com>, linux-mm@...ck.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH v3 27/34] mm: pagewalk: Add 'depth' parameter to pte_hole

On 2/27/19 9:06 AM, Steven Price wrote:
>  #ifdef CONFIG_SHMEM
>  static int smaps_pte_hole(unsigned long addr, unsigned long end,
> -		struct mm_walk *walk)
> +			  __always_unused int depth, struct mm_walk *walk)
>  {

I think this 'depth' argument is a mistake.  It's synthetic and it's
surely going to be a source of bugs.

The page table dumpers seem to be using this to dump out the "name" of a
hole which seems a bit bogus in the first place.  I'd much rather teach
the dumpers about the length of the hole, "the hole is 0x12340000 bytes
long", rather than "there's a hole at this level".