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

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Message-ID: <47F404F1.30103@goop.org>
Date:	Wed, 02 Apr 2008 15:13:05 -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:
> On Wed, 2008-04-02 at 14:35 -0700, Jeremy Fitzhardinge wrote:
>   
>> 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.
>>     
>
> Wow.  So does Xen ever use PSE to map kernel data?  That sucks.
>   

Not at present.  But I'd like to change it to manage memory in largepage 
chunks so that we can.

> Yeah, but I'm just talking about hotplugged memory.  When we add it, we
> don't have to map the added pages (since they're highmem) and don't have
> to touch their contents and zero them out, either.  Then, the balloon
> driver can notice that the memory is too large, and start to balloon it
> down.
>   

I didn't think x86-64 had a notion of highmem.

How do you prevent the pages from being used before they're ballooned out?

>> Everything also applies to x86-64.
>>     
>
> Not really, though.  We don't have the page->flags shortage or lack of
> vmemmap on x86_64.

Right now, I'd rather have a single mechanism that works for both.

    J
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