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

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Message-Id: <20081106105918.e64b7afb.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 6 Nov 2008 10:59:18 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Nigel Cunningham <ncunningham@...a.org.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	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 Thu, 6 Nov 2008 10:54:53 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Thu, 06 Nov 2008 12:43:07 +1100
> Nigel Cunningham <ncunningham@...a.org.au> wrote:
> 
> > Hi.
> > 
> > On Thu, 2008-11-06 at 10:17 +0900, KAMEZAWA Hiroyuki wrote:
> > > On Thu, 6 Nov 2008 09:14:41 +0900
> > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > > 
> > > > Ok, please consider "when memory hotplug happens." 
> > > > 
> > > > In general, it happens when
> > > >   1. memory is inserted to slot.
> > > >   2. the firmware notifes the system to enable already inserted memory.
> > > > 
> > > > To trigger "1", you have to open cover of server/pc. Do you open pc while the system
> > > > starts hibernation ? for usual people, no.
> > > > 
> > > > To trigger "2", the user have special console to tell firmware "enable this memory".
> > > > Such firmware console or users have to know "the system works well." And, more important,
> > > > when the system is suspended, the firmware can't do hotplug because the kernel is sleeping.
> > > > So, such firmware console or operator have to know the system status.
> > > > 
> > > > Am I missing some ? Current linux can know PCI/USB hotplug while the system is suspended ?
> > > > 
> > > *OFFTOPIC*
> > > 
> > > I hear following answer from my friend.
> > > 
> > >   - hibernate the system
> > > 	=> plug USB memory
> > > 		=> wake up the system
> > > 			=> panic.
> > >   - hibernate the system
> > > 	=> unplug USB memory
> > > 		=> wake up the sytem
> > > 			=> panic.
> > 
> > We currently check that the number of physical pages is the same when
> > starting to load the image, so neither of these issues cause real
> > problems.
> > 
> Hmm? this doesn't come from lost of hotplug interrupt ?
> the memory plugged while the system is sleeping can be recognized when the system wakes up ?
> 
> My point is the firmware/operator has to know "the system is sleeping or not" to do *any* hotplug.
> (I'm not sure but removing a cpu while the system is under hibernation may cause panic, too.)
> In my point of view, this is operator's problem, not hibernation's.

IOW,  please just remove !HIBERNATION in Kconfig and add "WARNING" to Documentaion.
for *now*.

I hope some notifier_call_chain from hibernation will be added.


Thanks,
-Kame

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