Re: [PATCH 1/2] mm, memory_hotplug: fix MMOP_ONLINE_KEEP behavior

[Vlastimil Babka]

On 06/01/2017 10:37 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> Heiko Carstens has noticed that the MMOP_ONLINE_KEEP is broken currently
> $ grep . memory3?/valid_zones
> memory34/valid_zones:Normal Movable
> memory35/valid_zones:Normal Movable
> memory36/valid_zones:Normal Movable
> memory37/valid_zones:Normal Movable
> 
> $ echo online_movable > memory34/state
> $ grep . memory3?/valid_zones
> memory34/valid_zones:Movable
> memory35/valid_zones:Movable
> memory36/valid_zones:Movable
> memory37/valid_zones:Movable
> 
> $ echo online > memory36/state
> $ grep . memory3?/valid_zones
> memory34/valid_zones:Movable
> memory36/valid_zones:Normal
> memory37/valid_zones:Movable
> 
> so we have effectivelly punched a hole into the movable zone. The
> problem is that move_pfn_range() check for MMOP_ONLINE_KEEP is wrong.
> It only checks whether the given range is already part of the movable
> zone which is not the case here as only memory34 is in the zone. Fix
> this by using allow_online_pfn_range(..., MMOP_ONLINE_KERNEL) if that
> is false then we can be sure that movable onlining is the right thing to
> do.
> 
> Reported-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Tested-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Fixes: "mm, memory_hotplug: do not associate hotadded memory to zones until online"

Just fold it there before sending to Linus, right?

> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  mm/memory_hotplug.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0a895df2397e..b3895fd609f4 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -950,11 +950,12 @@ static struct zone * __meminit move_pfn_range(int online_type, int nid,
>  	if (online_type == MMOP_ONLINE_KEEP) {
>  		struct zone *movable_zone = &pgdat->node_zones[ZONE_MOVABLE];
>  		/*
> -		 * MMOP_ONLINE_KEEP inherits the current zone which is
> -		 * ZONE_NORMAL by default but we might be within ZONE_MOVABLE
> -		 * already.
> +		 * MMOP_ONLINE_KEEP defaults to MMOP_ONLINE_KERNEL but use
> +		 * movable zone if that is not possible (e.g. we are within
> +		 * or past the existing movable zone)
>  		 */
> -		if (zone_intersects(movable_zone, start_pfn, nr_pages))
> +		if (!allow_online_pfn_range(nid, start_pfn, nr_pages,
> +					MMOP_ONLINE_KERNEL))
>  			zone = movable_zone;
>  	} else if (online_type == MMOP_ONLINE_MOVABLE) {
>  		zone = &pgdat->node_zones[ZONE_MOVABLE];
>