linux-kernel - Re: [PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining

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Date:	Wed, 02 Apr 2008 14:35:42 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH RFC] hotplug-memory: refactor online_pages to separate
 zone growth from page onlining

Dave Hansen wrote:
> Oh, once we've let Linux establish ptes to it, we've required that the
> hypervisor have it around?  How does that work with the balloon driver?
> Do we destroy the ptes when giving balloon memory back to the
> hypervisor?
>   

Yep.  It removes any mapping before handing it back to the hypervisor.

> If we're talking about i386, then we're set.  We don't map the hot-added
> memory at all because we only add highmem on i386.  The only time we map
> these pages is *after* we actually allocate them when they get mapped
> into userspace or used as vmalloc() or they're kmap()'d.
>   

Well, the balloon driver can balloon out lowmem pages, so we have to 
deal with mappings either way.  But balloon+hotplug would work 
identically on x86-64, so all pages are mapped.

>> I think we're getting off track here; this is a lot of extra complexity 
>> to justify allowing usermode to use /sys to online a chunk of hotplugged 
>> memory.
>>     
>
> Either that, or we're going to develop the entire Xen/kvm memory hotplug
> architecture around the soon-to-be-legacy i386 limitations. :)

Everything also applies to x86-64.


    J
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