netdev - Re: [net-next PATCH 4/4] net: frag LRU list per CPU

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Message-ID: <1366855546.8964.125.camel@edumazet-glaptop>
Date:	Wed, 24 Apr 2013 19:05:46 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	netdev@...r.kernel.org
Subject: Re: [net-next PATCH 4/4] net: frag LRU list per CPU

On Wed, 2013-04-24 at 17:25 -0700, Eric Dumazet wrote:

> We know that a slow sender has no chance to complete a packet if the
> attacker can create new fragments fast enough : frag_evictor() will keep
> the attacker fragments in memory and throw away good fragments.
> 

By the way, the frag_evictor() idea of cleaning 20% or 30% of the frags
simply doesn't scale to thousands of fragments.

It adds huge latencies in softirq context.

If we really want to evict old fragments before expiration timer, then
we can introduce a garbage collector in a work queue, and remove the
need of a timer per fragment.


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