linux-kernel - Re: [PATCH] Memory hot added,The memory can not been added to movable zone

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Date:	Wed, 19 Aug 2015 16:50:29 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Changsheng Liu <liuchangsheng@...pur.com>
Cc:	<isimatu.yasuaki@...fujitsu.com>, <vbabka@...e.cz>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<yanxiaofeng@...pur.com>, Changsheng Liu <liuchangcheng@...pur.com>
Subject: Re: [PATCH] Memory hot added,The memory can not been added to
 movable zone

On Wed, 19 Aug 2015 04:18:26 -0400 Changsheng Liu <liuchangsheng@...pur.com> wrote:

> From: Changsheng Liu <liuchangcheng@...pur.com>
> 
> When memory hot added, the function should_add_memory_movable
> always return 0,because the movable zone is empty,
> so the memory that hot added will add to normal zone even if
> we want to remove the memory.
> So we change the function should_add_memory_movable,if the user
> config CONFIG_MOVABLE_NODE it will return 1 when
> movable zone is empty

I cleaned this up a bit:

: Subject: mm: memory hot-add: memory can not been added to movable zone
: 
: 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.
: 
: So we change should_add_memory_movable(): if the user config
: CONFIG_MOVABLE_NODE it will return 1 when the movable zone is empty.

But I don't understand the "even if we want to remove the memory". 
This is hot-add, not hot-remove.  What do you mean here?

> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1198,9 +1198,13 @@ 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 (zone_is_empty(movable_zone))
> +	if (zone_is_empty(movable_zone)) {
> +	#ifdef CONFIG_MOVABLE_NODE
> +		return 1;
> +	#else
>  		return 0;
> -
> +	#endif
> +	}
>  	if (movable_zone->zone_start_pfn <= start_pfn)
>  		return 1;

Cleaner:

--- a/mm/memory_hotplug.c~memory-hot-addedthe-memory-can-not-been-added-to-movable-zone-fix
+++ a/mm/memory_hotplug.c
@@ -1181,13 +1181,9 @@ static int should_add_memory_movable(int
 	pg_data_t *pgdat = NODE_DATA(nid);
 	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
 
-	if (zone_is_empty(movable_zone)) {
-	#ifdef CONFIG_MOVABLE_NODE
-		return 1;
-	#else
-		return 0;
-	#endif
-	}
+	if (zone_is_empty(movable_zone))
+		return IS_ENABLED(CONFIG_MOVABLE_NODE);
+
 	if (movable_zone->zone_start_pfn <= start_pfn)
 		return 1;
 
_

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