netdev - Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash table

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Date:	Thu, 14 Mar 2013 08:10:40 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash
 table

On Thu, 2013-03-14 at 02:37 +0100, Hannes Frederic Sowa wrote:

> [PATCH net] inet: limit length of fragment queue hash table bucket lists
> 
> This patch introduces a constant limit of the fragment queue hash
> table bucket list lengths. Currently the limit 128 is choosen somewhat
> arbitrary and just ensures that we can fill up the fragment cache with
> empty packets up to the default ip_frag_high_thresh limits. It should
> just protect from list iteration eating considerable amounts of cpu.
> 
> If we reach the maximum length in one hash bucket a warning is printed.
> This is implemented on the caller side of inet_frag_find to distinguish
> between the different users of inet_fragment.c.

I like the idea of having a safe guard on the fragment queue hash table
bucket list lengths.  But I'm considering another cleanup/evictor
strategy, where we drop the LRU list, and do frag eviction on a hash
bucket level (which will be more cache optimal).  This strategy would
also involve a list length limit.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer


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