Re: RFC: MTU for serving NFS on Infiniband

[Marc Aurele La France]

On Tue, 24 Aug 2010, Ben Hutchings wrote:
> On Tue, 2010-08-24 at 09:14 -0600, Marc Aurele La France wrote:
> > On Mon, 23 Aug 2010, Stephen Hemminger wrote:
> > > On Mon, 23 Aug 2010 08:44:37 -0600 (MDT)
> > > Marc Aurele La France <tsi@xxxxxxxxxxx> wrote:
> > > > In regrouping for my next tack at this, I noticed that all stack traces go
> > > > through ip_append_data().  This would be ipv6_append_data() in the IPv6 case.
> > > > A _very_ rough draft that would have ip_append_data() temporarily drop down
> > > > to a smaller fake MTU follows ...

> > > Why doesn't NFS generate page size fragments?  Does Infiniband or your
> > > device not support this?  Any thing that requires higher order allocation
> > > is going to unstable under load.  Let's fix the cause not the apply bandaid
> > > solution to the symptom.

> > From what I can tell, IP fragmentation is done centrally.
> [...]

> Stephen and I are not talking about IP fragmentation, but about the
> ability to append 'fragments' to an skb rather than putting the entire
> packet payload in a linear buffer.  See
> <http://vger.kernel.org/~davem/skb_data.html>.

Any payload has to either fit in the MTU, or has to be broken up into 
MTU-sized (or less) fragments, come hell or high water.  That this is done 
centrally is a good thing.  It is the "(or less)" part that I am working 
towards here.

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                          |                                  |
+----------------------------------+----------------------------------+
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/