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

Vlastimil Babka
2015-08-20T07:42:04Z

On 08/20/2015 09:28 AM, Changsheng Liu wrote:
> From: Changsheng Liu <liuchangcheng@inspur.com>
>
> 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?

> 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@linux-foundation.org>
> Signed-off-by: Changsheng Liu <liuchangcheng@inspur.com>
> Tested-by: Dongdong Fan <fandd@inspur.com>
> ---
> 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;
>
>