linux-kernel - Re: [PATCH] hibernate / memory hotplug: always use for_each_populated

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Message-ID: <4A64E1D6.8090102@crca.org.au>
Date:	Tue, 21 Jul 2009 07:29:58 +1000
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>
Subject: Re: [PATCH] hibernate / memory hotplug: always use	for_each_populated_zone()

Hi.

Gerald Schaefer wrote:
> From: Gerald Schaefer <gerald.schaefer@...ibm.com>
> 
> Use for_each_populated_zone() instead of for_each_zone() in hibernation
> code. This fixes a bug on s390, where we allow both config options
> HIBERNATION and MEMORY_HOTPLUG, so that we also have a ZONE_MOVABLE
> here. We only allow hibernation if no memory hotplug operation was
> performed, so in fact both features can only be used exclusively, but
> this way we don't need 2 differently configured (distribution) kernels.
> 
> If we have an unpopulated ZONE_MOVABLE, we allow hibernation but run
> into a BUG_ON() in memory_bm_test/set/clear_bit() because hibernation
> code iterates through all zones, not only the populated zones, in
> several places. For example, swsusp_free() does for_each_zone() and
> then checks for pfn_valid(), which is true even if the zone is not
> populated, resulting in a BUG_ON() later because the pfn cannot be
> found in the memory bitmap.

I agree with your logic and patch, but doesn't this also imply that the
s390 implementation pfn_valid should be changed to return false for
those pages?

Regards,

Nigel
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