netdev - Re: [net-next PATCH V2 1/9] net: frag evictor, avoid killing warm frag queues

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Date:	Fri, 30 Nov 2012 06:57:25 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	David Miller <davem@...emloft.net>, 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,
	David Laight <David.Laight@...LAB.COM>
Subject: Re: [net-next PATCH V2 1/9] net: frag evictor, avoid killing warm
 frag queues

On Fri, 2012-11-30 at 13:01 +0100, Jesper Dangaard Brouer wrote:

> As the existing entries in the frag queues, are still being allowed
> packets through (even when the memory limit is exceeded).   In
> worst-case, as DaveM explained, this can be as much as 100KBytes per
> entry (for 64K fragments).

Some NIC uses a plain page to hold an ethernet frame.

Consider an UDP packet using 512 bytes frags, the resulting packet after
reassembly can use 128 pages. Thats 512 KB of memory on x86.



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