Re: [PATCH V8] mm: memory hot-add: hot-added memory can not be added to movable zone by default

[Changsheng Liu <liuchangsheng@inspur.com>]

a?? 2015/11/5 0:31, Dave Hansen a??e??:
> On 11/04/2015 12:23 AM, liuchangsheng wrote:
>> After the user config CONFIG_MOVABLE_NODE,
>> When the memory is hot added, should_add_memory_movable() return 0
>> because all zones including ZONE_MOVABLE are empty,
>> so the memory that was hot added will be assigned to ZONE_NORMAL,
>> and we need using the udev rules to online the memory automatically:
>> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline",
>> ATTR{state}="online_movable"
>> The memory block onlined by udev must be adjacent to ZONE_MOVABLE.
>> The events of memory section are notified to udev asynchronously,
>> so it can not ensure that the memory block onlined by udev is
>> adjacent to ZONE_MOVABLE.So it can't ensure memory online always success.
>> But we want the whole node to be added to ZONE_MOVABLE by default.
> I'm still a bit confused about the whole scenario here.
>
> Is the core problem:
> 1. We add memory in a new node and that node can not be made entirely
>     movable?
     As I know, System will not ensure that the node can be made 
entirely movable if the memory of
the node is assigned to ZONE_NORMAL
> or
> 2. We add memory to an existing zone that has some non-movable memory
>     and we want the new memory to be movable?
      It will work if we want to let the memroy movable by using 
movable_node
>
>> @@ -1201,6 +1201,9 @@ static int check_hotplug_memory_range(u64 start, u64 size)
>>   /*
>>    * If movable zone has already been setup, newly added memory should be check.
>>    * If its address is higher than movable zone, it should be added as movable.
>> + * And if system boots up with movable_node and config CONFIG_MOVABLE_NOD and
>> + * added memory does not overlap the zone before MOVABLE_ZONE,
>> + * the memory is added as movable.
>>    * Without this check, movable zone may overlap with other zone.
>>    */
> This comment is describing what the code does, but is rather sparse on
> why.  This scenario is pretty convoluted and I can barely make sense of
> why it is doing this today while looking at the whole changelog, much
> less in a few years when the original changelog will be harder to come by.
>
> Also please put the comment next to the new if() statement.  It's really
> hard to match the comment to the code the way you have it now.
>
>>   static int should_add_memory_movable(int nid, u64 start, u64 size)
>> @@ -1208,6 +1211,10 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
>>   	unsigned long start_pfn = start >> PAGE_SHIFT;
>>   	pg_data_t *pgdat = NODE_DATA(nid);
>>   	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
>> +	struct zone *pre_zone = pgdat->node_zones + (ZONE_MOVABLE - 1);
>> +
>> +	if (movable_node_is_enabled() && (zone_end_pfn(pre_zone) <= start_pfn))
>> +		return 1;
>>   
>>   	if (zone_is_empty(movable_zone))
>>   		return 0;
>>
> .
>

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