Re: RFC: MTU for serving NFS on Infiniband

[Eric Dumazet]

Le mardi 24 aoÃt 2010 Ã 13:49 -0600, Marc Aurele La France a Ãcrit :

> 
> 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.
> 

Could you post a full stack trace, to help me understand the path from
NFS to ip_append_data ?

I suspect this is UDP transport ?

This reminds me a patch I wrote for IPV6 : We were allocating a huge
(MTU sized) buffer, just to fill few bytes in it...


commit 72e09ad107e78d69ff4d3b97a69f0aad2b77280f
Author: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date:   Sat Jun 5 03:03:30 2010 -0700

    ipv6: avoid high order allocations
    
    With mtu=9000, mld_newpack() use order-2 GFP_ATOMIC allocations, that
    are very unreliable, on machines where PAGE_SIZE=4K
    
    Limit allocated skbs to be at most one page. (order-0 allocations)
    
    Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>


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