Re: [PATCH] Remove OOM killer from try_to_free_pages / all_unreclaimable braindamage

From: Chris Ross (chris_at_tebibyte.org)
Date: 11/18/04

  • Next message: George Anzinger: "Re: summary (Re: [patch] prefer TSC over PM Timer)" 
    Date:	Thu, 18 Nov 2004 00:27:15 +0100
To: Werner Almesberger <wa@almesberger.net>

    Werner Almesberger escreveu:
    > A process could declare itself as usual suspect. This would then be
    > recorded as a per-task flag, to be inherited by children.

    I don't think this "I know I'm buggy, please kill me" flag is the right
    approach even if it can be made to work. The operating system has an
    overview of all the memory and can see when a particular process is
    basically making the machine unusable. It's quite likely that the
    process causing the trouble doesn't know (or hasn't admitted) that it's
    buggy and hasn't volunteered for early termination. As this means the
    kernel must be able to deal with a problematic process completely
    irrespective of whether it has set "kill me" flag or not the flag
    doesn't really buy you anything.

    It is also specific to runaway processes that are clearly at fault.
    There is the related case where no particular process is faulty as such
    but the system as a whole can't cope with the demands being made.

    On a related note, I would prefer to see victim processes who are not
    determined to be the cause of the trouble swapped out (i.e. *all* their
    pages pushed out to swap) and suspended (not allowed to run) as a first
    resort. The example I have in mind is on my machine when the daily cron
    run over commits causing standard daemons such as ntpd to be killed to
    make room. It would be preferable if the daemon was swapped out and just
    didn't run for minutes, or even hours if need be, but was allowed to run
    again once the system had settled down.

    Of course, from recent discussion the system should not actually be
    killing off these daemons at all but that does seem to be resolved now.
    There are circumstances when there simply isn't enough RAM and swapping
    something out is preferable to killing it off. Of course, if there isn't
    sufficient swap space killing it should be the second resort. The last
    resort being panic.

    So, the problem breaks down into three parts:

              i) When should the oom killer be invoked.
             ii) How do we pick a victim process
            iii) How can we deal with the process in the most useful manner

    Regards,
    Chris R.

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