linux-kernel - Re: [PATCH] mm: add an option to disable bounce

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Message-ID: <20130422174712.GS14496@n2100.arm.linux.org.uk>
Date:	Mon, 22 Apr 2013 18:47:12 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	vinayakm.list@...il.com
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	rientjes@...gle.com
Subject: Re: [PATCH] mm: add an option to disable bounce

On Mon, Apr 22, 2013 at 08:53:00PM +0530, vinayakm.list@...il.com wrote:
> From: Vinayak Menon <vinayakm.list@...il.com>
> 
> There are times when HIGHMEM is enabled, but
> we don't prefer CONFIG_BOUNCE to be enabled.
> CONFIG_BOUNCE can reduce the block device
> throughput, and this is not ideal for machines
> where we don't gain much by enabling it. So
> provide an option to deselect CONFIG_BOUNCE. The
> observation was made while measuring eMMC throughput
> using iozone on an ARM device with 1GB RAM.
> 
> Signed-off-by: Vinayak Menon <vinayakm.list@...il.com>
> ---
>  mm/Kconfig |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 3bea74f..29f9736 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -263,8 +263,14 @@ config ZONE_DMA_FLAG
>  	default "1"
>  
>  config BOUNCE
> +	bool "Enable bounce buffers"
>  	def_bool y
>  	depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)

I don't think this is correct.  You shouldn't use "bool" with "def_bool".
Sure, add the "bool", but also change "def_bool" to "default".
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