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Subject: Re: [PATCH v3 27/34] mm: pagewalk: Add 'depth' parameter to pte_hole
To:     Steven Price <steven.price@arm.com>, linux-mm@kvack.org
Cc:     Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        James Morse <james.morse@arm.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Mark Rutland <Mark.Rutland@arm.com>,
        "Liang, Kan" <kan.liang@linux.intel.com>
References: <20190227170608.27963-1-steven.price@arm.com>
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From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <aece3046-6040-e2ec-fcd7-204113d40eb7@intel.com>
Date:   Wed, 27 Feb 2019 09:38:48 -0800
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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".