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Subject: Re: [PATCH] mem-hotplug: Use nodes that contain memory as mask in
 new_node_page()
References: <1473044391.4250.19.camel@TP420>
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From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <e9d15685-c484-8dd3-6a8f-9bfeedac9ac9@suse.cz>
Date: Wed, 21 Sep 2016 11:34:14 +0200
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Sender: owner-linux-mm@kvack.org
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To: Li Zhong <zhong@linux.vnet.ibm.com>, David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.cz>, linux-mm <linux-mm@kvack.org>, jallen@linux.vnet.ibm.com, qiuxishi@huawei.com, iamjoonsoo.kim@lge.com, n-horiguchi@ah.jp.nec.com, Andrew Morton <akpm@linux-foundation.org>, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>

On 09/21/2016 10:38 AM, Li Zhong wrote:
> Commit 9bb627be47a5 ("mem-hotplug: don't clear the only node in
> new_node_page()") prevents allocating from an empty nodemask, but as David
> points out, it is still wrong. As node_online_map may include memoryless
> nodes, only allocating from these nodes is meaningless.

Right, those pesky memoryless nodes...

> This patch uses node_states[N_MEMORY] mask to prevent the above case.

Suggested-by: David Rientjes <rientjes@google.com>

> Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/memory_hotplug.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b58906b..9d29ba0 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1555,8 +1555,8 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  {
>  	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
>  	int nid = page_to_nid(page);
> -	nodemask_t nmask = node_online_map;
> -	struct page *new_page;
> +	nodemask_t nmask = node_states[N_MEMORY];
> +	struct page *new_page = NULL;
>
>  	/*
>  	 * TODO: allocate a destination hugepage from a nearest neighbor node,
> @@ -1567,14 +1567,14 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  		return alloc_huge_page_node(page_hstate(compound_head(page)),
>  					next_node_in(nid, nmask));
>
> -	if (nid != next_node_in(nid, nmask))
> -		node_clear(nid, nmask);
> +	node_clear(nid, nmask);
>
>  	if (PageHighMem(page)
>  	    || (zone_idx(page_zone(page)) == ZONE_MOVABLE))
>  		gfp_mask |= __GFP_HIGHMEM;
>
> -	new_page = __alloc_pages_nodemask(gfp_mask, 0,
> +	if (!nodes_empty(nmask))
> +		new_page = __alloc_pages_nodemask(gfp_mask, 0,
>  					node_zonelist(nid, gfp_mask), &nmask);
>  	if (!new_page)
>  		new_page = __alloc_pages(gfp_mask, 0,
>
>

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