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

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Message-Id: <1225817945.12673.602.camel@nimitz>
Date:	Tue, 04 Nov 2008 08:59:05 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Tue, 2008-11-04 at 17:34 +0100, Rafael J. Wysocki wrote:
> 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.]

We currently don't have any big switch to disable memory hotplug, like
lock_memory_hotplug() or something. :)

If you are simply scanning and counting pages, I think the best thing to
use would be the zone_span_seq*() seqlock stuff.  Do your count inside
the seqlock's while loop.  That covers detecting a zone changing while
it is being scanned.

The other case to detect is when a new zone gets added.  These are
really rare.  Rare enough that we actually use a stop_machine() call in
build_all_zonelists() to do it.  All you would have to do is detect when
one of these calls gets made.  I think that's a good application for a
new seq_lock.

I've attached an utterly untested patch that should do the trick.
Yasunori and KAME should probably take a look at it since the node
addition code is theirs.

-- Dave

View attachment "zone-list-seqlock.patch" of type "text/x-patch" (1359 bytes)