linux-kernel - Re: [PATCH 1/1] memhp: Add hot-added memory ranges to memblock before allocate node

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Date:	Mon, 24 Aug 2015 17:22:54 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Tang Chen <tangchen@...fujitsu.com>
CC:	<akpm@...ux-foundation.org>, <isimatu.yasuaki@...fujitsu.com>,
	<n-horiguchi@...jp.nec.com>, <vbabka@...e.cz>,
	<mgorman@...hsingularity.net>, <rientjes@...gle.com>,
	<kamezawa.hiroyu@...fujitsu.com>, <izumi.taku@...fujitsu.com>,
	<yasu.isimatu@...il.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] memhp: Add hot-added memory ranges to memblock before
 allocate node_data for a node.

On 2015/8/24 1:06, Tang Chen wrote:

> The commit below adds hot-added memory range to memblock, after
> creating pgdat for new node.
> 
> commit f9126ab9241f66562debf69c2c9d8fee32ddcc53
> Author: Xishi Qiu <qiuxishi@...wei.com>
> Date:   Fri Aug 14 15:35:16 2015 -0700
> 
>     memory-hotplug: fix wrong edge when hot add a new node
> 
> But there is a problem:
> 
> add_memory()
> |--> hotadd_new_pgdat()
>      |--> free_area_init_node()
>           |--> get_pfn_range_for_nid()
>                |--> find start_pfn and end_pfn in memblock
> |--> ......
> |--> memblock_add_node(start, size, nid)    --------    Here, just too late.
> 
> get_pfn_range_for_nid() will find that start_pfn and end_pfn are both 0.
> As a result, when adding memory, dmesg will give the following wrong message.
> 
> [ 2007.577000] Initmem setup node 5 [mem 0x0000000000000000-0xffffffffffffffff]
> [ 2007.584000] On node 5 totalpages: 0
> [ 2007.585000] Built 5 zonelists in Node order, mobility grouping on.  Total pages: 32588823
> [ 2007.594000] Policy zone: Normal
> [ 2007.598000] init_memory_mapping: [mem 0x60000000000-0x607ffffffff]
> 
> The solution is simple, just add the memory range to memblock a little earlier,
> before hotadd_new_pgdat().
> 
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
>  mm/memory_hotplug.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6da82bc..9b78aff 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1248,6 +1248,14 @@ int __ref add_memory(int nid, u64 start, u64 size)
>  
>  	mem_hotplug_begin();
>  
> +	/*
> +	 * Add new range to memblock so that when hotadd_new_pgdat() is called to
> +	 * allocate new pgdat, get_pfn_range_for_nid() will be able to find this
> +	 * new range and calculate total pages correctly. The range will be remove
> +	 * at hot-remove time.
> +	 */
> +	memblock_add_node(start, size, nid);
> +

Hi Tang,

Looks fine to me.

If we add memblock_add_node() here, we should reset the managed pages and present pages,
so please revert my patch which Andrew has already merged into mm-tree.
"[PATCH 2/2] memory-hotplug: remove reset_node_managed_pages() and reset_node_managed_pages() in hotadd_new_pgdat()"

Thanks,
Xishi Qiu

>  	new_node = !node_online(nid);
>  	if (new_node) {
>  		pgdat = hotadd_new_pgdat(nid, start);
> @@ -1277,7 +1285,6 @@ int __ref add_memory(int nid, u64 start, u64 size)
>  
>  	/* create new memmap entry */
>  	firmware_map_add_hotplug(start, start + size, "System RAM");
> -	memblock_add_node(start, size, nid);
>  
>  	goto out;
>  
> @@ -1286,6 +1293,7 @@ error:
>  	if (new_pgdat)
>  		rollback_node_hotadd(nid, pgdat);
>  	release_memory_resource(res);
> +	memblock_remove(start, size);
>  
>  out:
>  	mem_hotplug_done();



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