Re: [RFC][PATCH 0/3] TCP/IP Critical socket communication mechanism

[Nick Piggin <nickpiggin@yahoo.com.au>]

David S. Miller wrote:
> From: Matt Mackall <mpm@selenic.com>
> Date: Wed, 14 Dec 2005 21:02:50 -0800
>
>
> > There needs to be two rules:
> >
> > iff global memory critical flag is set
> > - allocate from the global critical receive pool on receive
> > - return packet to global pool if not destined for a socket with an
> >  attached send mempool
>
>
> This shuts off a router and/or firewall just because iSCSI or NFS peed
> in it's pants.  Not really acceptable.

But that should only happen (shut off a router and/or firewall) in cases
where we now completely deadlock and never recover, including shutting off
the router and firewall, because they don't have enough memory to recv
packets either.

> > I think this will provide the desired behavior
>
>
> It's not desirable.
>
> What if iSCSI is protected by IPSEC, and the key management daemon has
> to process a security assosciation expiration and negotiate a new one
> in order for iSCSI to further communicate with it's peer when this
> memory shortage occurs?  It needs to send packets back and forth with
> the remove key management daemon in order to do this, but since you
> cut it off with this critical receive pool, the negotiation will never
> succeed.

I guess IPSEC would be a critical socket too, in that case. Sure
there is nothing we can do if the daemon insists on allocating lots
of memory...

> This stuff won't work.  It's not a generic solution and that's
> why it has more holes than swiss cheese. :-)

True it will have holes. I think something that is complementary and
would be desirable is to simply limit the amount of in-flight writeout
that things like NFS allows (or used to allow, haven't checked for a
while and there were noises about it getting better).

--
SUSE Labs, Novell Inc.

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