linux-kernel - Re: [PATCH v3 2/2] mm: Introduce kernelcore=mirror option

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Message-ID: <567241BE.5030806@jp.fujitsu.com>
Date:	Thu, 17 Dec 2015 14:01:50 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	"Izumi, Taku" <izumi.taku@...fujitsu.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mel@....ul.ie" <mel@....ul.ie>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v3 2/2] mm: Introduce kernelcore=mirror option

On 2015/12/17 13:48, Xishi Qiu wrote:
> On 2015/12/17 10:53, Kamezawa Hiroyuki wrote:
> 
>> On 2015/12/17 11:47, Xishi Qiu wrote:
>>> On 2015/12/17 9:38, Izumi, Taku wrote:
>>>
>>>> Dear Xishi,
>>>>
>>>>    Sorry for late.
>>>>
>>>>> -----Original Message-----
>>>>> From: Xishi Qiu [mailto:qiuxishi@...wei.com]
>>>>> Sent: Friday, December 11, 2015 6:44 PM
>>>>> To: Izumi, Taku/泉 拓
>>>>> Cc: Luck, Tony; linux-kernel@...r.kernel.org; linux-mm@...ck.org; akpm@...ux-foundation.org; Kamezawa, Hiroyuki/亀澤 寛
>>>>> 之; mel@....ul.ie; Hansen, Dave; matt@...eblueprint.co.uk
>>>>> Subject: Re: [PATCH v3 2/2] mm: Introduce kernelcore=mirror option
>>>>>
>>>>> On 2015/12/11 13:53, Izumi, Taku wrote:
>>>>>
>>>>>> Dear Xishi,
>>>>>>
>>>>>>> Hi Taku,
>>>>>>>
>>>>>>> Whether it is possible that we rewrite the fallback function in buddy system
>>>>>>> when zone_movable and mirrored_kernelcore are both enabled?
>>>>>>
>>>>>>     What does "when zone_movable and mirrored_kernelcore are both enabled?" mean ?
>>>>>>
>>>>>>     My patchset just provides a new way to create ZONE_MOVABLE.
>>>>>>
>>>>>
>>>>> Hi Taku,
>>>>>
>>>
>>> Hi Taku,
>>>
>>> We can NOT specify kernelcore= "nn[KMG]" and "mirror" at the same time.
>>> So when we use "mirror", in fact, the movable zone is a new zone. I think it is
>>> more appropriate with this name "mirrored zone", and also we can rewrite the
>>> fallback function in buddy system in this case.
>>
>> kernelcore ="mirrored zone" ?
> 
> No, it's zone_names[MAX_NR_ZONES]
> How about "Movable", -> "Non-mirrored"?
> 
That will break many user apps. I think we don't have enough reason. 

>>
>> BTW, let me confirm.
>>
>>    ZONE_NORMAL = mirrored
>>    ZONE_MOVABLE = not mirrored.
>>
> 
> Yes,
> 
>> so, the new zone is "not-mirrored" zone.
>>
>> Now, fallback function is
>>
>>     movable -> normal -> DMA.
>>
>> As Tony requested, we may need a knob to stop a fallback in "movable->normal", later.
>>
> 
> If the mirrored memory is small and the other is large,
> I think we can both enable "non-mirrored -> normal" and "normal -> non-mirrored".

Size of mirrored memory can be configured by software(EFI var).
So, having both is just overkill and normal->non-mirroed fallback is meaningless considering
what the feature want to guarantee.

Thanks,
-Kame




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