linux-kernel - Re: [PATCH] VMware Balloon driver

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Message-ID: <4BBE0C07.1000306@goop.org>
Date:	Thu, 08 Apr 2010 10:01:59 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Pavel Machek <pavel@....cz>
CC:	Avi Kivity <avi@...hat.com>, Dmitry Torokhov <dtor@...are.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pv-drivers@...are.com" <pv-drivers@...are.com>
Subject: Re: [PATCH] VMware Balloon driver

On 04/07/2010 10:30 PM, Pavel Machek wrote:
> Hi!
>
>   
>>>> 1) is not a huge amount of code, but something consistent would be  
>>>> nice.  2) is something we've been missing and is a bit of an open  
>>>> question/research project anyway.
>>>>         
>>> 3) Code that attempts to reclaim 2MB pages when possible
>>>       
>> Yes.  Ballooning in 4k units is a bit silly.
>>     
> Does it make sense to treat ballooning as a form of memory hotplug? 
>   

It has some similarities.  The main difference is granularity;
ballooning works in pages (typically 4k, but 2M probably makes more
sense), whereas memory hotplug works in DIMM-like sizes (256MB+). 
That's way too coarse for us; a domain might only have 256MB or less to
start with.

I experimented with a sort of hybrid scheme, in which I used hotplug
memory to add new struct pages to the system, but only incrementally
populated the underlying pages with the balloon driver.  That worked
pretty well, but it doesn't fit very well with how memory hotplug works
(at least when I last looked at it a couple of years ago).

    J
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