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    SubjectRe: Some questions about linux kernel.
    On Tue, 14 Mar 2000, Peter T. Breuer wrote:

    > "A month of sundays ago Jason Gunthorpe wrote:"
    > > On Mon, 13 Mar 2000, James Sutherland wrote:
    > > > I want to emphasise this point: the OOM handler should **NEVER** be
    > > > invoked. If it is ever needed, there is something BADLY wrong with the
    > > > system - either we do something drastic (process slaughtering) or the
    > > > machine goes down completely. Worrying about which user processes are
    > >
    > > Just as someone who has been bitten by this, I agree with James. The
    > > number one priority is keeping the machine up - I don't care what you
    > > kill, just keep it running and preferably allow remote logins still...
    >
    > The problem is that it is the process killer that is killing the
    > system, nothing else.
    >
    > The usual scenarios here are:
    >
    > a) httpd goes nuts because of some random bug and spawns 250 copies
    > of itself and sits there humming. System begins to drag, sendmail
    > begins to have trouble, connects start timing out leading to more
    > sendmail reconnects and more sendmail processes. Procmail can't
    > launch to do local deliver modes and sendmail throttling kicks
    > in producing bursts of process creation, followed by procmail
    > waiting forever on a single lock. Meanwhile nfs exports become
    > clogged and the system begins to labour ....
    >
    > Cure: knock out httpd.

    Yes.

    > b) Someone leaves netscape running unattached. It tears up the network
    > connection somehow. Networking begins to die, daemons like nfsd
    > and named start to loop internally, memory drops, error messages
    > spawned and can't be sent. Process killer kicks in. Kills cron,
    > nfsd or mountd, inetd or init (in order of probability, as far as
    > I can make out). System dead, won't reboot or take logins.
    >
    > Cure: stop the process killer. Things will just about work
    > forever in this state. Not well, but forever.

    No. Process killer kills Netscape (and anything else which has exploded as
    a result). Again, correct remedy. nfsd etc. will only be killed if they
    have already malfunctioned - I would rather have no nfsd running than a
    broken one, since a watchdog script can much more easily restart a fresh
    nfsd if the old one has gone.


    James.


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