netdev - Re: [PATCH net-next] flowcache: Tune per cpu flow cache shrink size

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Message-ID: <20140314102625.GJ32371@secunet.com>
Date:	Fri, 14 Mar 2014 11:26:25 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Fan Du <fan.du@...driver.com>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] flowcache: Tune per cpu flow cache shrink size

On Fri, Mar 14, 2014 at 03:42:46PM +0800, Fan Du wrote:
> When per cpu flow cache entries count reaches over high_watermark,
> flow cache will be shrinked gently to around low_watermark, not
> brutally killing most of cached entries by left only two.
> 

We currently keep two entries per hash bucket, this means that
we keep low_watermark entries at most in the flow cache.

With your change, we would keep low_watermark entries per hash bucket.
The flow cache would grow to low_watermark * flow_cache_hash_size then.
This would make DoS attacks against the flow cache quite easy.

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