linux-kernel - Re: [PATCH v2] cma: make default CMA area size zero for x86

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Date:	Mon, 06 Oct 2014 12:04:32 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Akinobu Mita <akinobu.mita@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Jean Delvare <jdelvare@...e.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Don Dutile <ddutile@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Yinghai Lu <yinghai@...nel.org>, x86@...nel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH v2] cma: make default CMA area size zero for x86

Hello,

On 2014-10-05 15:54, Akinobu Mita wrote:
> This makes CMA memory area size zero for x86 in default configuration
> (doesn't change on the other architectures).  If default CMA size is
> zero, DMA_CMA is disabled.  It can be enabled by passing cma= to the
> kernel.
>
> This makes less impact on x86.  Because there is no mainline driver that
> requires it for x86, and Peter Hurley reported the performance
> regression, as this is trying to drive _all_ dma mapping allocations
> through a _very_ small window.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Reported-by: Peter Hurley <peter@...leysoftware.com>
> Cc: Peter Hurley <peter@...leysoftware.com>
> Cc: Chuck Ebbert <cebbert.lkml@...il.com>
> Cc: Jean Delvare <jdelvare@...e.de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Don Dutile <ddutile@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> Cc: x86@...nel.org
> Cc: iommu@...ts.linux-foundation.org

Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
> * v2
> - Add information in help text, suggested by Chuck Ebbert
>
>   drivers/base/Kconfig | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 4e7f0ff..115882f 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -240,18 +240,24 @@ comment "Default contiguous memory area size:"
>   config CMA_SIZE_MBYTES
>   	int "Size in Mega Bytes"
>   	depends on !CMA_SIZE_SEL_PERCENTAGE
> +	default 0 if X86
>   	default 16
>   	help
>   	  Defines the size (in MiB) of the default memory area for Contiguous
> -	  Memory Allocator.
> +	  Memory Allocator.  If the size of 0 is selected, CMA is disabled by
> +	  default, but it can be enabled by passing cma=size[MG] to the kernel.
> +
>   
>   config CMA_SIZE_PERCENTAGE
>   	int "Percentage of total memory"
>   	depends on !CMA_SIZE_SEL_MBYTES
> +	default 0 if X86
>   	default 10
>   	help
>   	  Defines the size of the default memory area for Contiguous Memory
>   	  Allocator as a percentage of the total memory in the system.
> +	  If 0 percent is selected, CMA is disabled by default, but it can be
> +	  enabled by passing cma=size[MG] to the kernel.
>   
>   choice
>   	prompt "Selected region size"

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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