linux-kernel - Re: [PATCH v5 0/5] Add movablecore

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Message-ID: <1358208301.14145.118.camel@misato.fc.hp.com>
Date:	Mon, 14 Jan 2013 17:05:01 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Tang Chen <tangchen@...fujitsu.com>, jiang.liu@...wei.com,
	wujianguo@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	linfeng@...fujitsu.com, yinghai@...nel.org,
	isimatu.yasuaki@...fujitsu.com, rob@...dley.net,
	kosaki.motohiro@...fujitsu.com, minchan.kim@...il.com,
	mgorman@...e.de, rientjes@...gle.com, guz.fnst@...fujitsu.com,
	rusty@...tcorp.com.au, lliubbo@...il.com, jaegeuk.hanse@...il.com,
	tony.luck@...el.com, glommer@...allels.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 0/5] Add movablecore_map boot option

On Mon, 2013-01-14 at 14:34 -0800, Andrew Morton wrote:
> On Mon, 14 Jan 2013 09:31:33 -0800
> "H. Peter Anvin" <hpa@...or.com> wrote:
> 
> > On 01/14/2013 01:15 AM, Tang Chen wrote:
> > >
> > > For now, users can disable this functionality by not specifying the boot option.
> > > Later, we will post SRAT support, and add another option value "movablecore_map=acpi"
> > > to using SRAT.
> > >
> > 
> > I still think the option "movablecore_map" is uglier than hell.  "core" 
> > could just as easily refer to CPU cores there, but it is a memory mem. 
> > "movablemem" seems more appropriate.
> > 
> > Again, without SRAT I consider this patchset to be largely useless for 
> > anything other than prototyping work.
> > 
> 
> hm, why.  Obviously SRAT support will improve things, but is it
> actually unusable/unuseful with the command line configuration?

I think it is useful for prototyping and testing.  I do not think it is
suitable for regular users.

> Also, "But even if we can use SRAT, users still need an interface to
> enable/disable this functionality if they don't want to loose their
> NUMA performance.  So I think, an user interface is always needed."

Yes, but such user interface could be provided through the management
interface (GUI/CLI) of the platforms (or VMs).  If user sets for
performance, SRAT could be generated with no hot-pluggable memory.  If
user sets node N to be hot-removable, SRAT could be generated in such
way that all memory ranges in node N are hot-pluggable.

Thanks,
-Toshi


> There's also the matter of other architectures.  Has any thought been
> given to how (eg) powerpc would hook into here?
> 
> And what about VMs (xen, KVM)?  I wonder if there is a case for those
> to implement memory hotplug.  
> --
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