Re: [PATCH V4] mm: memory hot-add: memory can not be added to movable zone defaultly

From: Vlastimil Babka
Date: Mon Aug 31 2015 - 09:09:11 EST

On 08/31/2015 07:58 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.

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.
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>
Reviewed-by: Yasuaki Ishimatsu <yasu.isimatu@xxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Xiaofeng Yan <yanxiaofeng@xxxxxxxxxx>

Thanks for the credit for commenting on the previous versions of the patch. However, "Reviewed-by" currently means that the reviewer believes the patch is OK, so you can add it only if the reviewer offers it explicitly. See Documentation/SubmittingPatches section 13. There was a discussion on ksummit-discuss about adding a new tag for this case, but nothing was decided yet AFAIK.

Signed-off-by: Changsheng Liu <liuchangcheng@xxxxxxxxxx>
Tested-by: Dongdong Fan <fandd@xxxxxxxxxx>
mm/memory_hotplug.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 26fbba7..d1149ff 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1197,6 +1197,11 @@ 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 *normal_zone = pgdat->node_zones + ZONE_NORMAL;
+ if (movable_node_is_enabled()
+ && (zone_end_pfn(normal_zone) <= start_pfn))
+ return 1;

I wonder if the condition is true and ZONE_NORMAL exists (but it's empty?) if you intend to only add movable memory to a node, so you can still hot-remove it all with this patch?

if (zone_is_empty(movable_zone))
return 0;

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