Re: [Xen-devel] [PATCH net-next] xen-netfront: try linearizing SKB if it occupies too many slots

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, May 16, 2014 at 08:22:19AM -0700, Eric Dumazet wrote:
> On Fri, 2014-05-16 at 15:36 +0100, Wei Liu wrote:
> > On Fri, May 16, 2014 at 07:21:08AM -0700, Eric Dumazet wrote:
> > > On Fri, 2014-05-16 at 14:11 +0100, Wei Liu wrote:
> > > 
> > > > It's not that common to trigger this, I only saw a few reports. In fact
> > > > Stefan's report is the first one that comes with a method to reproduce
> > > > it.
> > > > 
> > > > I tested with redis-benchmark on a guest with 256MB RAM and only saw a
> > > > few "failed to linearize", never saw a single one with 1GB guest.
> > > 
> > > Well, I am just saying. This is asking order-5 allocations, and yes,
> > > this is going to fail after few days of uptime, no matter what you try.
> > > 
> > 
> > Hmm... I see what you mean -- memory fragmentation leads to allocation
> > failure. Thanks.
> 
> In the mean time, have you tried to lower gso_max_size ?
> 
> Setting it witk netif_set_gso_max_size() to something like 56000 might
> avoid the problem.
> 
> (Not sure if it is applicable in your case)
> 

It works, at least in this Redis testcase. Could you explain a bit where
this 56000 magic number comes from? :-)

Presumably I can derive it from some constant in core network code?

Wei.

> 

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