linux-kernel - RE: [PATCH 2/2] Drivers: hv: Add Hyper-V balloon driver

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Date:	Wed, 10 Oct 2012 02:26:46 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>
Subject: RE: [PATCH 2/2] Drivers: hv: Add Hyper-V balloon driver



> -----Original Message-----
> From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> Sent: Tuesday, October 09, 2012 9:15 PM
> To: KY Srinivasan
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> andi@...stfloor.org
> Subject: Re: [PATCH 2/2] Drivers: hv: Add Hyper-V balloon driver
> 
> On Wed, 10 Oct 2012 00:09:12 +0000 KY Srinivasan <kys@...rosoft.com> wrote:
> 
> > > > +		if (!pg) {
> > > > +			*alloc_error = true;
> > > > +			return i * alloc_unit;
> > > > +		}
> > > > +
> > > > +		totalram_pages -= alloc_unit;
> > >
> > > Well, I'd consider totalram_pages to be an mm-private thing which drivers
> > > shouldn't muck with.  Why is this done?
> >
> > By modifying the totalram_pages, the information presented in /proc/meminfo
> > correctly reflects what is currently assigned to the guest (MemTotal).
> 
> eh?  /proc/meminfo:MemTotal tells you the total memory in the machine.
> The only thing which should change it after boot is memory hotplug.
> 
> Modifying it in this manner puts the statistic into a state know as
> "wrong".  And temporarily modifying it in this fashion will cause the
> tremendous amount of initialisation code which relies upon
> totalram_pages for sizing to also enter the "wrong" state.
> 
> Why on earth do balloon drivers do this?  If the amount of memory which
> is consumed by balloons is interesting then it should be exported via a
> standalone metric, not by mucking with totalram_pages.

I see your point. I will get rid of the code that manipulates the totalram_pages.

Regards,

K. Y
 


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