Re: [PATCH V2] mm:memory hot-add: memory can not been added to movable zone

From: Changsheng Liu
Date: Thu Aug 20 2015 - 22:00:58 EST



On 08/20/201515:41, Vlastimil Babka wrote:
On 08/20/2015 09:28 AM, Changsheng Liu wrote:
From: Changsheng Liu <liuchangcheng@xxxxxxxxxx>

When memory is hot added, should_add_memory_movable() always returns 0
because the movable zone is empty, so the memory that was hot added will
add to the normal zone even if we want to remove the memory.

I'm not expert on memory hot-plug, but since you CC'd me, I wonder... the function has this comment: " * If movable zone has already been setup, newly added memory should be check."

So I read it like "if you want movable memory *at all*, you should do some setup first" (but don't ask me what setup). After your patch, every hot-added memory would be automatically movable? Isn't that silently changing behavior against user expectations? What about those that don't want to hot-remove and don't want movable zones (which limit what kind of allocations are possible), is there a way to prevent memory being movable after your patch?
After the system startup, we hot added one cpu with memory, The function arch_add_memory() will add the memory to
normal zone defaultly but now all zones including normal zone and movable zone are empty.So If we want to add the memory
to movable zone we need change should_add_memory_movable().

So we change should_add_memory_movable(): if the user config
CONFIG_MOVABLE_NODE it will return 1 when the movable zone is empty.

Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Changsheng Liu <liuchangcheng@xxxxxxxxxx>
Tested-by: Dongdong Fan <fandd@xxxxxxxxxx>
---
mm/memory_hotplug.c | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 26fbba7..ff658f2 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1199,8 +1199,7 @@ static int should_add_memory_movable(int nid, u64 start, u64 size)
struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;

if (zone_is_empty(movable_zone))
- return 0;
-
+ return IS_ENABLED(CONFIG_MOVABLE_NODE);
if (movable_zone->zone_start_pfn <= start_pfn)
return 1;



.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/