linux-kernel - Re: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN

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Date:   Wed, 4 Jan 2017 13:28:31 +0000
From:   Will Deacon <will.deacon@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, catalin.marinas@....com,
        akpm@...ux-foundation.org, hanjun.guo@...aro.org,
        xieyisheng1@...wei.com, rrichter@...ium.com, james.morse@....com
Subject: Re: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA

On Wed, Dec 14, 2016 at 09:11:47AM +0000, Ard Biesheuvel wrote:
> The NUMA code may get confused by the presence of NOMAP regions within
> zones, resulting in spurious BUG() checks where the node id deviates
> from the containing zone's node id.
> 
> Since the kernel has no business reasoning about node ids of pages it
> does not own in the first place, enable CONFIG_HOLES_IN_ZONE to ensure
> that such pages are disregarded.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  arch/arm64/Kconfig | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 111742126897..0472afe64d55 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -614,6 +614,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>  	def_bool y
>  	depends on NUMA
>  
> +config HOLES_IN_ZONE
> +	def_bool y
> +	depends on NUMA
> +
>  source kernel/Kconfig.preempt
>  source kernel/Kconfig.hz

I'm happy to apply this, but I'll hold off until the first patch is queued
somewhere, since this doesn't help without the VM_BUG_ON being moved.

Alternatively, I can queue both if somebody from the mm camp acks the
first patch.

Will