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

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Date:	Thu, 27 Aug 2015 11:29:52 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Changsheng Liu <liuchangsheng@...pur.com>,
	akpm@...ux-foundation.org, isimatu.yasuaki@...fujitsu.com
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, wunan@...pur.com,
	yanxiaofeng@...pur.com, fandd@...pur.com,
	Changsheng Liu <liuchangcheng@...pur.com>
Subject: Re: [PATCH V3] mm: memory hot-add: memory can not be added to movable
 zone defaultly

On 08/27/2015 10:54 AM, Changsheng Liu wrote:
> From: Changsheng Liu <liuchangcheng@...pur.com>
>
> 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.

> 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@...ux-foundation.org>

Interesting...

> Signed-off-by: Changsheng Liu <liuchangcheng@...pur.com>i
> Tested-by: Dongdong Fan <fandd@...pur.com>
> ---
>   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;
>
>

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