linux-kernel - Re: [linux-pm] [PATCH] hibernation should work ok with memory hotplug

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Message-Id: <200811041734.04802.rjw@sisk.pl>
Date:	Tue, 4 Nov 2008 17:34:03 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Nigel Cunningham <ncunningham@...a.org.au>,
	Matt Tolentino <matthew.e.tolentino@...el.com>,
	linux-pm@...ts.osdl.org, Dave Hansen <haveblue@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, pavel@...e.cz,
	Mel Gorman <mel@...net.ie>, Andy Whitcroft <apw@...dowen.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] [PATCH] hibernation should work ok with memory hotplug

On Tuesday, 4 of November 2008, Dave Hansen wrote:
> On Tue, 2008-11-04 at 16:35 +0100, Rafael J. Wysocki wrote:
> > On Tuesday, 4 of November 2008, Dave Hansen wrote:
> > > On Tue, 2008-11-04 at 09:54 +0100, Rafael J. Wysocki wrote:
> > > > To handle this, I need to know two things:
> > > > 1) what changes of the zones are possible due to memory hotplugging
> > > > (i.e.    can they grow, shring, change boundaries etc.)
> > > 
> > > All of the above. 
> > 
> > OK
> > 
> > If I allocate a page frame corresponding to specific pfn, is it guaranteed to
> > be associated with the same pfn in future?
> 
> Page allocation is different.  Since you hold a reference to a page, it
> can not be removed until you release that reference.  That's why every
> normal alloc_pages() user in the kernel doesn't have to worry about
> memory hotplug.

Good. :-)

So, if I allocate the image pages right prior to creating the image, they
won't be touched by memory hotplug.

Now, I need to do one more thing, which is to check how much memory has to be
freed before creating the image.  For this purpose I need to lock memory
hotplug temporarily, count pages to free and unlock it.  What interface should
I use for this purpose? 

[I'll also need to lock memory hotplug temporarily during resume.]

Rafael
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