On 11/17/2018 07:50 AM, Wei Yang wrote:
> Function init_currently_empty_zone() will adjust pgdat->nr_zones and set
> it to 'zone_idx(zone) + 1' unconditionally. This is correct in the
> normal case, while not exact in hot-plug situation.
>
> This function is used in two places:
>
> * free_area_init_core()
> * move_pfn_range_to_zone()
>
> In the first case, we are sure zone index increase monotonically. While
> in the second one, this is under users control.
So pgdat->nr_zones over counts the number of zones than what node has
really got ? Does it affect all online options (online/online_kernel
/online_movable) if there are other higher index zones present on the
node.
>
> One way to reproduce this is:
> ----------------------------
>
> 1. create a virtual machine with empty node1
>
> -m 4G,slots=32,maxmem=32G \
> -smp 4,maxcpus=8 \
> -numa node,nodeid=0,mem=4G,cpus=0-3 \
> -numa node,nodeid=1,mem=0G,cpus=4-7
>
> 2. hot-add cpu 3-7
>
> cpu-add [3-7]
>
> 2. hot-add memory to nod1
>
> object_add memory-backend-ram,id=ram0,size=1G
> device_add pc-dimm,id=dimm0,memdev=ram0,node=1
>
> 3. online memory with following order
>
> echo online_movable > memory47/state
> echo online > memory40/state
>
> After this, node1 will have its nr_zones equals to (ZONE_NORMAL + 1)
> instead of (ZONE_MOVABLE + 1).
Which prevents an over count I guess. Just wondering if you noticed this
causing any real problem or some other side effects.
>
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> ---
> mm/page_alloc.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b7cd20dbaef..2d3c54201255 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5823,8 +5823,10 @@ void __meminit init_currently_empty_zone(struct zone *zone,
> unsigned long size)
> {
> struct pglist_data *pgdat = zone->zone_pgdat;
> + int zone_idx = zone_idx(zone) + 1;
>
> - pgdat->nr_zones = zone_idx(zone) + 1;
> + if (zone_idx > pgdat->nr_zones)
> + pgdat->nr_zones = zone_idx;
This seems to be correct if we try to init a zone (due to memory hotplug)
in between index 0 and pgdat->nr_zones on an already populated node.
