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

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Message-ID: <3b3b72db-32fd-446c-9971-e119a8993b3d@default>
Date:	Wed, 21 Nov 2012 07:26:58 -0800 (PST)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Konrad Wilk <konrad.wilk@...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

> From: Konrad Rzeszutek Wilk
> Sent: Tuesday, November 20, 2012 7:48 PM
> To: Dan Magenheimer
> 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.

OK, thanks!

> > 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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