linux-kernel - Re: [PATCH 5/4] x86/mm: Further simplify 1 GB kernel linear mappings handling

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Message-Id: <54F81C6D0200007800066757@mail.emea.novell.com>
Date:	Thu, 05 Mar 2015 08:05:49 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Ingo Molnar" <mingo@...nel.org>
Cc:	<luto@...capital.net>, <tony@...mide.com>,
	<david.vrabel@...rix.com>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>, <toshi.kani@...com>,
	<qiuxishi@...wei.com>, <x86@...nel.org>, <iamjoonsoo.kim@....com>,
	<tglx@...utronix.de>, <akpm@...ux-foundation.org>,
	<dave.hansen@...ux.intel.com>, <gregkh@...uxfoundation.org>,
	<julia.lawall@...6.fr>, <decui@...rosoft.com>, <mingo@...hat.com>,
	"Juergen Gross" <JGross@...e.com>,
	"Luis Rodriguez" <Mcgrof@...e.com>, <vbabka@...e.cz>, <bp@...e.de>,
	<pavel@....cz>, <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH 5/4] x86/mm: Further simplify 1 GB kernel linear
 mappings handling

>>> On 05.03.15 at 08:23, <mingo@...nel.org> wrote:

> It's a bit pointless to allow Kconfig configuration for 1GB kernel
> mappings, it's already hidden behind a 'default y' and CONFIG_EXPERT.
> 
> Remove this complication and simplify the code by renaming
> CONFIG_ENABLE_DIRECT_GBPAGES to CONFIG_X86_DIRECT_GBPAGES and
> document the DEBUG_PAGE_ALLOC and KMEMCHECK quirks.
> 
> Cc: Luis R. Rodriguez <mcgrof@...e.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Dexuan Cui <decui@...rosoft.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: JBeulich@...e.com 
> Cc: Jan Beulich <JBeulich@...e.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tony Lindgren <tony@...mide.com>
> Cc: Toshi Kani <toshi.kani@...com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Xishi Qiu <qiuxishi@...wei.com>
> Cc: julia.lawall@...6.fr 
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/Kconfig   | 23 +++++++----------------
>  arch/x86/mm/init.c |  7 +------
>  2 files changed, 8 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 4d06e1c8294a..54d528a37ff4 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1299,22 +1299,13 @@ config ARCH_DMA_ADDR_T_64BIT
>  	def_bool y
>  	depends on X86_64 || HIGHMEM64G
>  
> -config ENABLE_DIRECT_GBPAGES
> -	def_bool y
> -	depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK
> -
> -config DIRECT_GBPAGES
> -	bool "Enable 1GB pages for kernel pagetables" if EXPERT
> -	default y
> -	depends on ENABLE_DIRECT_GBPAGES
> -	---help---
> -	  Enable by default the kernel linear mapping to use 1GB pages on CPUs
> -	  that support it. This can improve the kernel's performance a tiny bit
> -	  by reducing TLB pressure. If in doubt, say "Y". If you've disabled
> -	  option but your platform is capable of handling support for this
> -	  you can use the gbpages kernel parameter. Likewise if you've enabled
> -	  this but you'd like to force disable this option you can use the
> -	  nogbpages kernel parameter.
> +config X86_DIRECT_GBPAGES
> +	def_bool (X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK)

config X86_DIRECT_GBPAGES
	def_bool y
	depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK

or else it'll leave a pointless

# CONFIG_X86_DIRECT_GBPAGES is not set

in .config-s where the dependencies are not met.

Jan

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