Messages in this thread | | | Date | Mon, 27 Jun 2005 15:17:09 +0200 | From | Pavel Machek <> | Subject | Re: [RFC] Fix SMP brokenness for PF_FREEZE and make freezing usable for other purposes |
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Hi!
> >CL> frozen(process) Check for frozen process > >CL> freezing(process) Check if a process is being frozen > >CL> freeze(process) Tell a process to freeze (go to > >refrigerator) > >CL> thaw_process(process) Restart process > > > >CL> I only know that this boots correctly since I have no system that can > >do > >CL> suspend. But Ray needs an effective means of process suspension for > >CL> his process migration patches. > > The process migration patches that Christoph mentions are avaialable at > > http://marc.theaimsgroup.com/?l=linux-mm&m=111945947315561&w=2 > > and subsequent notes to the -mm or lhms-devel lists. The problem there is > that this code depends on user space code to suspend and then resume the > processes to be migrated before/after the migration. Christoph suggested > using PF_FREEZE, but I pointed out that was broken on SMP so hence the > current patch. > > The idea would be to use PF_FREEZE to cause the process suspension. > A minor flaw in this approach is what happens if a process migration > is in progress when the machine is suspended/resumed. (Probably not > a common occurrence on Altix... :-), but anyway...). If the processes > are PF_FROZEN by the migration code, then unfrozen by the resume code, > and then the migration code continues, then we have unstopped processes > being migratated again. Not a good thing. On the other hand, the
Should be very easy to solve with one semaphore. Simply make swsusp wait until all migrations are done.
> Is the above scenario even possible? manual page migration runs as a system > call. Do system calls all complete before suspend starts? If that is > the case, then the above is not something to worry about.
Yes, are normal system calls complete before suspend starts -- but that's what refrigerator cares about.
> Finally, how comfortable are people about using the PF_FREEZE stuff > to start and resume processes for purposes unrelated to suspend/resume?
No problem with that...
BTW smp notebooks will come, sooner or later, and 2-core 2-way-HT notebook is already NUMA system. Pavel -- Boycott Kodak -- for their patent abuse against Java. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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