Subject: RE: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics

From: "Alex Aizman" <[email-masked]>
Date: Tue, 29 Mar 2005 18:28:25 -0800

Jamal wrote: 
> 
> > 
> > Eventually the TCP will hit its RTX limit and punt the connection, 
> > freeing the buffers kept for retransmission right?
> > 
> 
> If i read correctly the people arguing for iscsi say thats 
> not good enough. But they may be having other issues too...

It is not good enough for storage. 

If we continue to fall back into TCP-will-eventually-recover mentality
iSCSI, or at least a "soft" non-offloaded iSCSI over regular non-TOE TCP,
will not be able to compete with FC, which uses determinstic credit-based
flow control. That non-determinism is a bigger issue, while a corner case
like swap device happenning to be iSCSI-remote is just that, a corner case
that helps to highlight and bring the general problem to the foreground.

Adding a "critical" or "resource-protected" attribute to the connection
context is a step in the right  direction. Next steps include:

- triage (closing non-critical connections in OOM);
- socket reopen without deallocating memory (something like: close(int
socket_fd, int will_reopen));
- preallocated mempools (it is much better to discover OOM at connection
open time than well into runtime).
- better resource "counting" throughout the L3 and L4 layers to preventively
handle OOM;

And more incremental steps like that.

Alex