Re: [PATCH V2] mm:memory hot-add: memory can not been added to movable zone

[Changsheng Liu <liuchangsheng@inspur.com>]

First, thanks very much for your review, I will update codes according 
to your suggestion

On 2015/8/25 21:12, Yasuaki Ishimatsu wrote:
> On Thu, 20 Aug 2015 03:28:05 -0400
> Changsheng Liu <liuchangsheng@inspur.com> wrote:
>
>> From: Changsheng Liu <liuchangcheng@inspur.com>
>>
>> When memory is hot added, should_add_memory_movable() always returns 0
>> because the movable zone is empty, so the memory that was hot added will
>> add to the normal zone even if we want to remove the memory.
>>
>> So we change should_add_memory_movable(): if the user config
>> CONFIG_MOVABLE_NODE it will return 1 when the movable zone is empty.
>>
>> Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
>> Signed-off-by: Changsheng Liu <liuchangcheng@inspur.com>
>> Tested-by: Dongdong Fan <fandd@inspur.com>
>> ---
>>   mm/memory_hotplug.c |    3 +--
>>   1 files changed, 1 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 26fbba7..ff658f2 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1199,8 +1199,7 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
>>   	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
>>   
>>   	if (zone_is_empty(movable_zone))
>> -		return 0;
>> -
>> +		return IS_ENABLED(CONFIG_MOVABLE_NODE);
>>   	if (movable_zone->zone_start_pfn <= start_pfn)
>>   		return 1;
> Currently, kernel allows to create ZONE_MOVABLE after ZONE_NORMAL as follows:
>   PFN low                                 high
>         ---|-------------|-------------|---
>              ZONE_NORMAL   ZONE_MOVABLE
>
> But kernel does not allow to create ZONE_MOVABLE before ZONE_NORMAL as follows:
>   PFN low                                 high
>         ---|-------------|-------------|---
>              ZONE_MOVABLE  ZONE_NORMAL
>
> Also, kernel does not allow to create ZONE_MOVABLE in ZOME_NORMAL as follows:
>   PFN low                                              high
>         ---|-------------|-------------|-------------|---
>              ZONE_NORMAL   ZONE_MOVABLE  ZONE_NORMAL
>
> So should_add_memory_movable() checks them.
>
> Accoring to your patch, when movable_zone is empty, the hot added memory is
> always managed to ZONE_MOVABLE. It means that ZONE_MOVALBE will puts before/in
> ZONE_NORMAL.
>
> You must prevent from creating ZONE_MOVABLE before/in ZONE_NORMAL.
>
> Thanks,
> Yasuaki Ishimatsu
>
>>   
>> -- 
>> 1.7.1
>>
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