linux-kernel - Re: [Xen-devel] [PATCH RFC 01/12] xen-blkback: don't store dev_bus

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Message-ID: <51362516.1000600@citrix.com>
Date:	Tue, 5 Mar 2013 18:02:14 +0100
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH RFC 01/12] xen-blkback: don't store dev_bus_addr

On 05/03/13 09:06, Jan Beulich wrote:
>>>> On 04.03.13 at 18:19, Roger Pau Monné<roger.pau@...rix.com> wrote:
>> On 28/02/13 11:58, Jan Beulich wrote:
>>>>>> On 28.02.13 at 11:28, Roger Pau Monne <roger.pau@...rix.com> wrote:
>>> And then the biolist[] array really can be folded into a union
>>> with the remaining seg[] one, as their usage scopes are easily
>>> separable.
>>
>> Could we leave that for a further patch? I would like to avoid messing
>> any more with blkback, as I'm already touching a lot of bits with this
>> patch series.
> 
> Fine by me, but ...
> 
>>>> @@ -631,7 +629,8 @@ static int xen_blkbk_map(struct blkif_request *req,
>>>>  			if (ret)
>>>>  				continue;
>>>>  
>>>> -			seg[i].buf = persistent_gnts[i]->dev_bus_addr |
>>>> +			seg[i].buf = pfn_to_mfn(page_to_pfn(
>>>> +				persistent_gnts[i]->page)) << PAGE_SHIFT |
>>>
>>> So why do you do this? The only reader masks the field with
>>> ~PAGE_MASK anyway.
>>
>> Yes, I only need to store first_sect.
> 
> ... as you're touching this code anyway, and as it'll make the
> code as well as the patch smaller, could you at least drop this
> pointless storing of the page address (which otherwise I'd ask
> you to properly parenthesize anyway)?
> 
> And iirc once that's dropped, the storing of first_sect ends up
> being identical between the if and else bodies, so it could be
> pulled out (further reducing code size, albeit at the price of a
> marginally bigger patch).

Yes, I've already done that, thanks for the suggestion.

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