Re: RFC: MTU for serving NFS on Infiniband

[Marc Aurele La France]

On Thu, 26 Aug 2010, Eric Dumazet wrote:
> Le jeudi 26 aoÃt 2010 Ã 05:40 -0600, Marc Aurele La France a Ãcrit :

> > Steady now.  There's no need to YELL nor be arrogant.  You and I both know
> > there's a place for NFS over UDP.  That's not changing any time soon.  While
> > I'm aware of the issue you brought up, it is separate from the one at hand in
> > this discussion.

> > I do want to thank you, however, for reminding me of TCP.  It's something
> > 20/20 hindsight says I should have checked out before starting this thread.
> > Logistically, it'll be a few days before I can do so though.  If that allows
> > me to increase the MTU all the way up to 65520, then this UDP thing will
> > likely remain unresolved.

> Unfortunately, your infiniband device lacks NETIF_F_SG support.

Oh, the device itself probably has something similar, but ipoib 
(IP-over-Infiniband) doesn't export that capability.

> MTU a bit larger than PAGE_SIZE-overhead will need high order
> allocations ?

Right.  And a 65520 MTU allocates sk_buff's with 128K contiguous payloads.

Marc.

+----------------------------------+----------------------------------+
|  Marc Aurele La France           |  work:   1-780-492-9310          |
|  Academic Information and        |  fax:    1-780-492-1729          |
|    Communications Technologies   |  email:  tsi@xxxxxxxxxxx         |
|  352 General Services Building   +----------------------------------+
|  University of Alberta           |                                  |
|  Edmonton, Alberta               |    Standard disclaimers apply    |
|  T6G 2H1                         |                                  |
|  CANADA                          |                                  |
+----------------------------------+----------------------------------+