netdev - Re: [net-next PATCH V2 3/9] net: frag, move LRU list maintenance outside of rwlock

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Message-ID: <1354228431.11754.355.camel@localhost>
Date:	Thu, 29 Nov 2012 23:33:51 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Laight <David.Laight@...LAB.COM>
Cc:	David Miller <davem@...emloft.net>, fw@...len.de,
	netdev@...r.kernel.org, pablo@...filter.org, tgraf@...g.ch,
	amwang@...hat.com, kaber@...sh.net, paulmck@...ux.vnet.ibm.com,
	herbert@...dor.hengli.com.au
Subject: Re: [net-next PATCH V2 3/9] net: frag, move LRU list maintenance
 outside of rwlock

On Thu, 2012-11-29 at 09:54 -0800, Eric Dumazet wrote:
> On Thu, 2012-11-29 at 12:48 -0500, David Miller wrote:
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > Date: Thu, 29 Nov 2012 09:43:24 -0800
> > 
> > > Use a schem with a hash table of 256 (or 1024) slots.
> > > 
> > > Each slot/bucket has : 
> > >   - Its own spinlock.
> > >   - List of items
> > >   - A limit of 5 (or so) elems in the list.
> > > 
> > > No more LRU, no more rehash (thanks to jhash and the random seed at boot
> > > or first frag created), no more reader-writer lock.
> > > 
> > > Use a percpu_counter to implement ipfrag_low_thresh/ipfrag_high_thresh
> > 
> > If we limit the chain sizes to 5 elements, there is no need for
> > any thresholds at all.
> 
> One element can hold about 100KB.
> 
> I guess some systems could have some worries if we consume 1024 * 5 *
> 100 KB

1024 * 5 * 100k = 512 MB  -- That's just crasy!
I guess the embedded guys is going to choke reading this! 

Look at what I have achieved with 256KBytes per CPU...

--Jesper


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