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

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Date:	Thu, 12 Nov 2009 15:09:57 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mark Smith <lk-netdev@...netdev.nosense.org>
CC:	David Miller <davem@...emloft.net>, opurdila@...acom.com,
	shemminger@...tta.com, netdev@...r.kernel.org
Subject: Re: [PATCH] [next-next-2.6] net: configurable device name hash

Mark Smith a écrit :
> On Wed, 11 Nov 2009 18:36:26 -0800 (PST)
> David Miller <davem@...emloft.net> wrote:
> 
>> From: Octavian Purdila <opurdila@...acom.com>
>> Date: Wed, 11 Nov 2009 23:47:41 +0200
>>
>>> 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.
>> Use kzalloc(), that's sufficient for a 64K or so hash table which is
>> way more than you ever will need.
>>
>> Use the GFP_* flags that will silently (ie. without a log message)
>> fail, and divide by two until you successfully allocate the table if
>> you're worried about memory fragmentation at allocation time.
>>
>> This is so straightforward, I can't believe we're talking so much
>> about how to implement this, it's a 15 minute hack :-)
> 
> Yes, but sadly, sometimes there is too much history(!) to be able to be
> fully aware of it. "suck-it-and-see" type patches are possibly a
> quicker way to find out what people are thinking right now!
> 

Before extending hash tables, we should make sure existing algos are going to
scale with millions of netdevices, and they dont scale that much for the moment.
We still have many for_each_netdev() loops...

It's easy to change a constant somewhere in an include file, its less easy to make
real scalability changes :(

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