Re: [PATCH V4] mm: memory hot-add: memory can not be added to movable zone defaultly

[Vlastimil Babka <vbabka@suse.cz>]

On 08/31/2015 07:58 AM, Changsheng Liu wrote:
> From: Changsheng Liu <liuchangcheng@inspur.com>
>
> After the user config CONFIG_MOVABLE_NODE and movable_node kernel option,
> When the memory is hot added, should_add_memory_movable() return 0
> because all zones including movable zone are empty,
> so the memory that was hot added will be added  to the normal zone
> and the normal zone will be created firstly.
> But we want the whole node to be added to movable zone defaultly.
>
> So we change should_add_memory_movable(): if the user config
> CONFIG_MOVABLE_NODE and movable_node kernel option
> it will always return 1 and all zones is empty at the same time,
> so that the movable zone will be created firstly
> and then the whole node will be added to movable zone defaultly.
> If we want the node to be added to normal zone,
> we can do it as follows:
> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state"
>
> If the memory is added to movable zone defaultly,
> the user can offline it and add it to other zone again.
> But if the memory is added to normal zone defaultly,
> the user will not offline the memory used by kernel.
>
> Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
> Reviewed-by: Yasuaki Ishimatsu <yasu.isimatu@gmail.com>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> Reviewed-by: Xiaofeng Yan <yanxiaofeng@inspur.com>

Thanks for the credit for commenting on the previous versions of the 
patch. However, "Reviewed-by" currently means that the reviewer believes 
the patch is OK, so you can add it only if the reviewer offers it 
explicitly. See Documentation/SubmittingPatches section 13. There was a 
discussion on ksummit-discuss about adding a new tag for this case, but 
nothing was decided yet AFAIK.

> Signed-off-by: Changsheng Liu <liuchangcheng@inspur.com>
> Tested-by: Dongdong Fan <fandd@inspur.com>
> ---
>   mm/memory_hotplug.c |    5 +++++
>   1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 26fbba7..d1149ff 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1197,6 +1197,11 @@ 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 *normal_zone = pgdat->node_zones + ZONE_NORMAL;
> +
> +	if (movable_node_is_enabled()
> +	&& (zone_end_pfn(normal_zone) <= start_pfn))
> +		return 1;

I wonder if the condition is true and ZONE_NORMAL exists (but it's 
empty?) if you intend to only add movable memory to a node, so you can 
still hot-remove it all with this patch?

>
>   	if (zone_is_empty(movable_zone))
>   		return 0;
>