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

[Xishi Qiu <qiuxishi@huawei.com>]

On 2015/11/4 16:23, 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,

Hi Yasuaki,

If udev onlines memory in descending order, like 3->2->1->0, it will
success, but we notifiy to udev in ascending order, like 0->1->2->3,
so the udev rules cannot online memory as movable, right?

> 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.
> 
> So we change should_add_memory_movable(): if the user config
> CONFIG_MOVABLE_NODE and movable_node kernel option
> and the ZONE_NORMAL is empty or the pfn of the hot-added memory
> is after the end of the ZONE_NORMAL it will always return 1
> and then the whole node will be added to ZONE_MOVABLE by default.
> If we want the node to be assigned to ZONE_NORMAL,
> we can do it as follows:
> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state"
> 

The order should like 0->1->2->3, right? 3->2->1->0 will be failed.

> Signed-off-by: liuchangsheng <liuchangsheng@inspur.com>
> Signed-off-by: Xiaofeng Yan <yanxiaofeng@inspur.com>
> Tested-by: Dongdong Fan <fandd@inspur.com>
> Reviewed-by: <yasu.isimatu@gmail.com>
> Cc: Wang Nan <wangnan0@huawei.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: Tang Chen <tangchen@cn.fujitsu.com>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> Cc: Toshi Kani <toshi.kani@hp.com>
> Cc: Xishi Qiu <qiuxishi@huawei.com>
> ---
>  mm/memory_hotplug.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index aa992e2..8617b9f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -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.
>   */
>  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;
>  

Looks good to me.

How about add some comment in mm/Kconfig?

Thanks,
Xishi Qiu

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