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    SubjectRe: Some questions about linux kernel.
    On Wed, 15 Mar 2000, James Sutherland wrote:

    > On Wed, 15 Mar 2000, Paul Jakma wrote:
    > > so isn't what should be concentrated on? Per user limits are a cleaner
    > > way of fixing the problem.
    > They would AVOID the problem in a lot of cases - but not always.

    avoid is what i meant.. sorry..

    > Yes, we should have per-user resource limits. Yes, they would help
    > prevent malloc-bombs from being effective. No, they will not
    > *prevent* OOM situations arising.

    no they won't, of course not. risk of OOM is a feature of an
    overcommiting VM. no way round it.

    > > OOM is a stopgap. Ideally we should be able to set ironclad policies so
    > > that we never encounter OOM.
    > I doubt that could really be achieved. Dynamically reducing user rlimits
    > to try to prevent them overloading the system would ALMOST achieve this

    you could do it with a damon..

    > -
    > but what if a root process blows up? What if a couple of users all hit
    > their resource limits at once? While individually they may not have high
    > enough resource limits to OOM the box, a group of users would still be
    > able to.

    note that i said "be /able/ to". Ie If as admin could limit each user in
    @users to 50MB of address space on a 4 user box, then i just need to
    make sure that i have > 200MB of RAM+swap, to know that i will never OOM
    because of @user processes.

    most people though would accept more risk with potential OOM for more
    flexible VM usage.

    It'd be nice to have that choice. And i'm pretty sure per-user VM
    beancounting would allow me to pretty much reduce risk of OOM to close
    to 0 on my boxes..

    > make this almost impossible - but never completely.

    of course, i wouldn't suggest otherwise. OOM is a risk you take with
    just about every present day OS.

    > James.


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