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

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Message-ID: <1354211659.3299.15.camel@edumazet-glaptop>
Date:	Thu, 29 Nov 2012 09:54:19 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	brouer@...hat.com, 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 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

So lets call the threshold a limit ;)

I agree the ipfrag_low_thresh should disappear :

One we hit the ipfrag_high_thresh (under softirq), we really dont want
to scan table to perform gc, as it might take more than 10 ms




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