netdev - Re: [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped SKB fragments

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Message-ID: <530B4E05.4020900@schaman.hu>
Date:	Mon, 24 Feb 2014 13:49:57 +0000
From:	Zoltan Kiss <zoltan.kiss@...aman.hu>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	wei.liu2@...rix.com, xen-devel@...ts.xenproject.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	jonathan.davies@...rix.com
Subject: Re: [PATCH net-next v5 4/9] xen-netback: Change RX path for mapped
 SKB fragments

On 22/02/14 23:18, Zoltan Kiss wrote:
> On 18/02/14 17:45, Ian Campbell wrote:
>> On Mon, 2014-01-20 at 21:24 +0000, Zoltan Kiss wrote:
>>
>> Re the Subject: change how? Perhaps "handle foreign mapped pages on the
>> guest RX path" would be clearer.
> Ok, I'll do that.
>
>>
>>> RX path need to know if the SKB fragments are stored on pages from 
>>> another
>>> domain.
>> Does this not need to be done either before the mapping change or at the
>> same time? -- otherwise you have a window of a couple of commits where
>> things are broken, breaking bisectability.
> I can move this to the beginning, to keep bisectability. I've put it 
> here originally because none of these makes sense without the previous 
> patches.
Well, I gave it a close look: to move this to the beginning as a 
separate patch I would need to put move a lot of definitions from the 
first patch to here (ubuf_to_vif helper, xenvif_zerocopy_callback etc.). 
That would be the best from bisect point of view, but from patch review 
point of view even worse than now. So the only option I see is to merge 
this with the first 2 patches, so it will be even bigger. And based on 
that principle, patch #6 and #8 should be merged there as well, as they 
solve corner cases introduced by the grant mapping.
I don't know how much the bisecting requirements are written in stone. 
At this moment, all the separate patches compile, but after #2 there are 
new problems solved in #4, #6 and #8. If someone bisect in the middle of 
this range and run into these problems, they could quite easily figure 
out what went wrong looking at the adjacent patches. So I would 
recommend to keep this current order.
What's your opinion?

Zoli
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