linux-kernel - Re: [PATCH] xen: tmem: selfballooning should be enabled when xen tmem is enabled

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Date:	Tue, 20 Nov 2012 21:47:53 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org
Subject: Re: [PATCH] xen: tmem: selfballooning should be enabled when xen
 tmem is enabled

On Tue, Nov 20, 2012 at 02:42:18PM -0800, Dan Magenheimer wrote:
> Konrad: Any chance this can get in for the upcoming window?
> (Or is it enough of a bug fix that it can go in at an -rcN?)

Lets do it in the next merge window. About now I am comfortable
only with regression fixes.
> 
> It was just pointed out to me that some kernels have
> cleancache and frontswap and xen_tmem enabled but NOT
> xen_selfballooning!  While this configuration should be
> possible, nearly all kernels that have CONFIG_XEN_TMEM=y should
> also have CONFIG_XEN_SELFBALLOONING=y, since Transcendent
> Memory (tmem) for Xen has very limited value without
> selfballooning.
> 
> This is probably a result of a Kconfig mistake fixed I think
> by the patch below.  Note that the year-old Oracle UEK2 kernel
> distro has both CONFIG_XEN_TMEM and CONFIG_XEN_SELFBALLOONING
> enabled, as does a Fedora 17 kernel update (3.6.6-1.fc17), so
> the combination should be well tested.  Also, Xen tmem (and thus
> selfballooning) are currently only enabled when a kernel boot
> parameter is supplied so there is no runtime impact without
> that boot parameter.
> 
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> 
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index d4dffcd..b5f02f3 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -10,9 +10,9 @@ config XEN_BALLOON
>  	  return unneeded memory to the system.
>  
>  config XEN_SELFBALLOONING
> -	bool "Dynamically self-balloon kernel memory to target"
> -	depends on XEN && XEN_BALLOON && CLEANCACHE && SWAP && XEN_TMEM
> -	default n
> +	bool
> +	depends on XEN_BALLOON && SWAP
> +	default y if XEN_TMEM
>  	help
>  	  Self-ballooning dynamically balloons available kernel memory driven
>  	  by the current usage of anonymous memory ("committed AS") and
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