linux-kernel - Re: [RFC PATCH 00/12] mm: mirrored memory support for page buddy allocations

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Date:	Thu, 18 Jun 2015 11:55:42 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Xishi Qiu <qiuxishi@...wei.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, nao.horiguchi@...il.com,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	Xiexiuqi <xiexiuqi@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	"Luck, Tony" <tony.luck@...el.com>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/12] mm: mirrored memory support for page buddy
 allocations

On 06/18/2015 11:37 AM, Xishi Qiu wrote:
> On 2015/6/18 13:58, Vlastimil Babka wrote:
>
>> On 18.6.2015 3:23, Xishi Qiu wrote:
>>> On 2015/6/16 17:46, Vlastimil Babka wrote:
>>>
>>
>> On the other hand, it would skip just as inefficiently over MIGRATE_MIRROR
>> pageblocks within a Normal zone. Since migrating pages between MIGRATE_MIRROR
>> and other types pageblocks would violate what the allocations requested.
>>
>> Having separate zone instead would allow compaction to run specifically on the
>> zone and defragment movable allocations there (i.e. userspace pages if/when
>> userspace requesting mirrored memory is supported).
>>
>>>>
>>>
>>> Hi Vlastimil,
>>>
>>> If there are many mirror regions in one node, then it will be many holes in the
>>> normal zone, is this fine?
>>
>> Yeah, it doesn't matter how many holes there are.
>
> So mirror zone and normal zone will span each other, right?
>
> e.g. node 1: 4G-8G(normal), 8-12G(mirror), 12-16G(normal), 16-24G(mirror), 24-28G(normal) ...
> normal: start=4G, size=28-4=24G,
> mirror: start=8G, size=24-8=16G,

Yes, that works. It's somewhat unfortunate wrt performance that the 
hardware does it like this though.

> I think zone is defined according to the special address range, like 16M(DMA), 4G(DMA32),

Traditionally yes. But then there is ZONE_MOVABLE, this year's LSF/MM we 
discussed (and didn't outright deny) ZONE_CMA...
I'm not saying others will favour the new zone approach though, it's 
just my opinion that it might be a better option than a new migratetype.

> and is it appropriate to add a new mirror zone with a volatile physical address?

By "volatile" you mean what, that the example above would change 
dynamically? That would be rather challenging...

> Thanks,
> Xishi Qiu
>

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