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

[Xishi Qiu <qiuxishi@huawei.com>]

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 06/16/2015 10:17 AM, Xishi Qiu wrote:
>>>> On 2015/6/16 15:53, Vlastimil Babka wrote:
>>>>
>>>>> On 06/04/2015 02:54 PM, Xishi Qiu wrote:
>>>>>>
>>>>>> I think add a new migratetype is btter and easier than a new zone, so I use
>>>>>
>>>>> If the mirrored memory is in a single reasonably compact (no large holes) range
>>>>> (per NUMA node) and won't dynamically change its size, then zone might be a
>>>>> better option. For one thing, it will still allow distinguishing movable and
>>>>> unmovable allocations within the mirrored memory.
>>>>>
>>>>> We had enough fun with MIGRATE_CMA and all kinds of checks it added to allocator
>>>>> hot paths, and even CMA is now considering moving to a separate zone.
>>>>>
>>>>
>>>> Hi, how about the problem of this case:
>>>> e.g. node 0: 0-4G(dma and dma32)
>>>>      node 1: 4G-8G(normal), 8-12G(mirror), 12-16G(normal),
>>>> so more than one normal zone in a node? or normal zone just span the mirror zone?
>>>
>>> Normal zone can span the mirror zone just fine. However, it will result in zone
>>> scanners such as compaction to skip over the mirror zone inefficiently. Hmm...
> 
> 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,

I think zone is defined according to the special address range, like 16M(DMA), 4G(DMA32),
and is it appropriate to add a new mirror zone with a volatile physical address?

Thanks,
Xishi Qiu

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