netdev - Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

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Message-ID: <538F40EE.2040609@citrix.com>
Date:	Wed, 4 Jun 2014 16:53:18 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	David Laight <David.Laight@...LAB.COM>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"wei.liu2@...rix.com" <wei.liu2@...rix.com>,
	"paul.durrant@...rix.com" <paul.durrant@...rix.com>,
	"linux@...elenboom.it" <linux@...elenboom.it>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many
 slots

On 04/06/14 11:15, Zoltan Kiss wrote:
> On 04/06/14 09:50, David Laight wrote:
>> From: netdev-owner@...r.kernel.org
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers
>>> are fully
>>> utilized.
>> ...
>>> -static bool start_new_rx_buffer(int offset, unsigned long size, int
>>> head)
>>> +static bool start_new_rx_buffer(int offset,
>>> +                unsigned long size,
>>> +                int head,
>>> +                bool full_coalesce)
>>
>> The above is completely incorrect layout ...
> Can you elaborate a bit please on "above"?

I just realized you're not talking about skb layout but format. I'll fix 
that.

Zoli

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