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

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Date:	Thu, 29 Nov 2012 10:24:52 -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 13:05 -0500, David Miller wrote:

> Replace 1024 in your formula with X and the limit is therefore
> controlled by X.
> 
> So it seems the high_thresh can be replaced with an appropriate
> determination of X to size the hash.
> 
> If X is 256, that limits us to ~130MB per cpu.
> 

per host, as the table would be shared by all cpus.

Lets say the default mem limit would be 4MB, I believe the
percpu_counter is cheap enough that we still allow a 1024 buckets table,
and allow receiving full size IP packets (If not under frag attack)

(If we divided 4MB by 64, we would have a 64KB limit per bucket, which
is too small because of truesize overhead)


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