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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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