netdev - Re: [net-next PATCH 2/3] net: fix enforcing of fragment queue hash list depth

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Message-ID: <1366382991.16391.6.camel@edumazet-glaptop>
Date:	Fri, 19 Apr 2013 07:49:51 -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 2/3] net: fix enforcing of fragment queue hash
 list depth

On Fri, 2013-04-19 at 14:19 +0200, Jesper Dangaard Brouer wrote:

> When removing the LRU system (which is the real bottleneck, see perf
> tests in cover mail), and doing direct hash cleaning we are trading-in
> accuracy.
> 

You are mixing performance issues and correctness.

> The reason I don't want a too big hash table is the following.
> 

> Worst case 1024 buckets * 130K bytes = 133 MBytes, which on smaller
> embedded systems is a lot of kernel memory we are permitting a remote
> host to "lock-down".

Thats pretty irrelevant, memory is limited by the total amount of memory
used by fragments, not by hash table size.

Its called /proc/sys/net/ipv4/ipfrag_high_thresh

It seems you me you are spending time on wrong things.



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