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    SubjectRe: [PATCH v2]mm/oom-kill: direct hardware access processes should get bonus
    > On Sun, 14 Nov 2010, KOSAKI Motohiro wrote:
    > > > So the question that needs to be answered is: why do these threads deserve
    > > > to use 3% more memory (not >4%) than others without getting killed? If
    > > > there was some evidence that these threads have a certain quantity of
    > > > memory they require as a fundamental attribute of CAP_SYS_RAWIO, then I
    > > > have no objection, but that's going to be expressed in a memory quantity
    > > > not a percentage as you have here.
    > >
    > > 3% is choosed by you :-/
    > >
    > No, 3% was chosen in __vm_enough_memory() for LSMs as the comment in the
    > oom killer shows:
    > /*
    > * Root processes get 3% bonus, just like the __vm_enough_memory()
    > * implementation used by LSMs.
    > */
    > and is described in Documentation/filesystems/proc.txt.
    > I think in cases of heuristics like this where we obviously want to give
    > some bonus to CAP_SYS_ADMIN that there is consistency with other bonuses
    > given elsewhere in the kernel.

    Keep comparision apple to apple. vm_enough_memory() account _virtual_ memory.
    oom-killer try to free _physical_ memory. It's unrelated.

    > > Old background is very simple and cleaner.
    > >
    > The old heuristic divided the arbitrary badness score by 4 with
    > CAP_SYS_RESOURCE. The new heuristic doesn't consider it.
    > How is that more clean?
    > > CAP_SYS_RESOURCE mean the process has a privilege of using more resource.
    > > then, oom-killer gave it additonal bonus.
    > >
    > As a side-effect of being given more resources to allocate, those
    > applications are relatively unbounded in terms of memory consumption to
    > other tasks. Thus, it's possible that these applications are using a
    > massive amount of memory (say, 75%) and now with the proposed change a
    > task using 25% of memory would be killed instead. This increases the
    > liklihood that the CAP_SYS_RESOURCE thread will have to be killed
    > eventually, anyway, and the goal is to kill as few tasks as possible to
    > free sufficient amount of memory.

    You are talking two difference at once. 3% vs 4x and CAP_SYS_RESOURCE and

    Please keep comparing apple to apple.

    > Since threads having CAP_SYS_RESOURCE have full control over their
    > oom_score_adj, they can take the additional precautions to protect
    > themselves if necessary. It doesn't need to be a part of the heuristic to
    > bias these tasks which will lead to the undesired result described above
    > by default rather than intentionally from userspace.
    > > CAP_SYS_RAWIO mean the process has a direct hardware access privilege
    > > (eg, RDB). and then, killing it might makes system crash.
    > >
    > Then you would want to explicitly filter these tasks from oom kill just as
    > OOM_SCORE_ADJ_MIN works rather than giving them a memory quantity bonus.

    No. Why does userland recover your mistake?

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