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

David S. Miller wrote: 
From: Matt Mackall <mpm@xxxxxxxxxxx>
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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