linux-kernel - Re: RFC: MTU for serving NFS on Infiniband

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Date:	Tue, 24 Aug 2010 22:09:32 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Marc Aurele La France <tsi@...berta.ca>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: RFC: MTU for serving NFS on Infiniband

Le mardi 24 août 2010 à 13:49 -0600, Marc Aurele La France a écrit :

> 
> 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@...il.com>
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@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>


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