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    SubjectRe: [linux-pm] [PATCH] hibernation should work ok with memory hotplug
    On Thu, 6 Nov 2008 10:54:53 +0900
    KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

    > On Thu, 06 Nov 2008 12:43:07 +1100
    > Nigel Cunningham <ncunningham@crca.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@jp.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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