Re: [PATCH V3] mm: memory hot-add: memory can not be added to movable zone defaultly

From: Changsheng Liu
Date: Thu Aug 27 2015 - 07:07:35 EST

å 2015/8/27 17:29, Vlastimil Babka åé:
On 08/27/2015 10:54 AM, Changsheng Liu wrote:
From: Changsheng Liu <liuchangcheng@xxxxxxxxxx>

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.

OK it seems current behavior indeed goes against the expectations of setting movable_node.

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.

Was this tested to really work as well? Per Yasuaki's explanation in v2, you shouldn't create ZONE_MOVABLE before ZONE_NORMAL.
We will test it more fully.
There is on limit written in Documentation/memory-hotplug.txt when move the memory from movable zone to normal zone:
echo online_kernel > /sys/devices/system/memory/memoryXXX/state
(NOTE: current limit: this memory block must be adjacent to ZONE_NORMAL)

The zone will be created as follows:
First,all zones have been initialized,but all zones are empty, then the should_add_memory_movable() return 1 so the movable is created and add the whole node to movable zone.
empty whole node's memory

when we move the memory to normal zone
empty whole node's memory
one memory block ajacent to ZONE_NORMAL :
one memory block : whole node - one memory block

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@xxxxxxxxxxxxxxxxxxxx>


Signed-off-by: Changsheng Liu <liuchangcheng@xxxxxxxxxx>i
Tested-by: Dongdong Fan <fandd@xxxxxxxxxx>
mm/memory_hotplug.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 26fbba7..b5f14fa 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1198,6 +1198,9 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
pg_data_t *pgdat = NODE_DATA(nid);
struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;

+ if (movable_node_is_enabled())
+ return 1;
if (zone_is_empty(movable_zone))
return 0;


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at