Re: memory_hotplug: zone_can_shift() returns boolean value

[Reza Arbab]

On Mon, Dec 12, 2016 at 03:29:04PM -0500, Yasuaki Ishimatsu wrote:
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -410,15 +410,13 @@ static ssize_t show_valid_zones(struct device *dev,
> 	sprintf(buf, "%s", zone->name);
>
> 	/* MMOP_ONLINE_KERNEL */
> -	zone_shift = zone_can_shift(start_pfn, nr_pages, ZONE_NORMAL);
> -	if (zone_shift) {
> +	if (zone_can_shift(start_pfn, nr_pages, ZONE_NORMAL, &zone_shift)) {
> 		strcat(buf, " ");
> 		strcat(buf, (zone + zone_shift)->name);
> 	}
>
> 	/* MMOP_ONLINE_MOVABLE */
> -	zone_shift = zone_can_shift(start_pfn, nr_pages, ZONE_MOVABLE);
> -	if (zone_shift) {
> +	if (zone_can_shift(start_pfn, nr_pages, ZONE_MOVABLE, &zone_shift)) {
> 		strcat(buf, " ");
> 		strcat(buf, (zone + zone_shift)->name);
> 	}

You still need to check zone_shift != 0, otherwise you may get duplicate 
output:

$ cat /sys/devices/system/node/node1/memory256/valid_zones
Movable Normal Movable
$ cat /sys/devices/system/node/node1/memory257/valid_zones
Movable Movable

> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1033,8 +1033,8 @@ static void node_states_set_node(int node, struct memory_notify *arg)
> 	node_set_state(node, N_MEMORY);
> }
>
> -int zone_can_shift(unsigned long pfn, unsigned long nr_pages,
> -		   enum zone_type target)
> +bool zone_can_shift(unsigned long pfn, unsigned long nr_pages,
> +		   enum zone_type target, int *zone_shift)
> {
> 	struct zone *zone = page_zone(pfn_to_page(pfn));
> 	enum zone_type idx = zone_idx(zone);

I think you should initialize zone_shift here. It should be 0 if the 
function returns false.

	*zone_shift = 0;

> @@ -1043,26 +1043,27 @@ int zone_can_shift(unsigned long pfn, unsigned long nr_pages,
> 	if (idx < target) {
> 		/* pages must be at end of current zone */
> 		if (pfn + nr_pages != zone_end_pfn(zone))
> -			return 0;
> +			return false;
>
> 		/* no zones in use between current zone and target */
> 		for (i = idx + 1; i < target; i++)
> 			if (zone_is_initialized(zone - idx + i))
> -				return 0;
> +				return false;
> 	}
>
> 	if (target < idx) {
> 		/* pages must be at beginning of current zone */
> 		if (pfn != zone->zone_start_pfn)
> -			return 0;
> +			return false;
>
> 		/* no zones in use between current zone and target */
> 		for (i = target + 1; i < idx; i++)
> 			if (zone_is_initialized(zone - idx + i))
> -				return 0;
> +				return false;
> 	}
>
> -	return target - idx;
> +	*zone_shift = target - idx;
> +	return true;
> }
>
> /* Must be protected by mem_hotplug_begin() */
> @@ -1089,10 +1090,13 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
> 	    !can_online_high_movable(zone))
> 		return -EINVAL;
>
> -	if (online_type == MMOP_ONLINE_KERNEL)
> -		zone_shift = zone_can_shift(pfn, nr_pages, ZONE_NORMAL);
> -	else if (online_type == MMOP_ONLINE_MOVABLE)
> -		zone_shift = zone_can_shift(pfn, nr_pages, ZONE_MOVABLE);
> +	if (online_type == MMOP_ONLINE_KERNEL) {
> +		if (!zone_can_shift(pfn, nr_pages, ZONE_NORMAL, &zone_shift))
> +			return -EINVAL;
> +	} else if (online_type == MMOP_ONLINE_MOVABLE) {
> +		if (!zone_can_shift(pfn, nr_pages, ZONE_MOVABLE, &zone_shift))
> +			return -EINVAL;
> +	}
>
> 	zone = move_pfn_range(zone_shift, pfn, pfn + nr_pages);
> 	if (!zone)
> --
> 1.8.3.1

--
Reza Arbab