netdev - Re: [PATCH] [next-next-2.6] net: configurable device name hash

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Date:	Wed, 11 Nov 2009 23:47:41 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] [next-next-2.6] net: configurable device name hash

On Wednesday 11 November 2009 23:33:42 you wrote:
> On Wed, 11 Nov 2009 12:42:35 -0800 (PST)
> 
> David Miller <davem@...emloft.net> wrote:
> > From: Octavian Purdila <opurdila@...acom.com>
> > Date: Wed, 11 Nov 2009 21:38:44 +0200
> >
> > > I don't think we can dynamically size it at boot time since it
> > > depends on the usage pattern which is impossible to determine at
> > > boot time, right?
> >
> > We have no idea how many sockets will be used by the system yet we
> > dynamically size the socket hash tables.
> >
> > Please do some research and see how we handle this elsewhere in the
> > networking.
> 
> dcache also sizes hash bits at boot time on available memory.
> See alloc_large_system_hash().
> 

Thanks Stephen.

I was actually taking a look at that but I see that the device hash is 
allocated per net namespace which means we can't use 
alloc_large_system_hash().

We could use a similar function that will work in the per namespace 
initialization context, but this might upset net namespace folks since we will 
get a large hash for every namespace.

Not sure what can be done to address that problem now except using a boot 
parameter to override the defaults. A better solution would be to be able to 
use "namespace create" parameters but it appears we don't have this 
possibility, yet.

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