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    SubjectRe: RFC: MTU for serving NFS on Infiniband
    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@ualberta.ca> 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.

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