linux-kernel - Re: [PATCH 2/2] memory-hotplug: remove reset_node_managed_pages() and reset_node_managed_pages() in hotadd_new

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Date:	Sun, 23 Aug 2015 18:28:06 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	<izumi.taku@...fujitsu.com>
CC:	<tangchen@...fujitsu.com>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Yasuaki Ishimatsu <yasu.isimatu@...il.com>
Subject: Re: [PATCH 2/2] memory-hotplug: remove reset_node_managed_pages()
 and reset_node_managed_pages() in hotadd_new_pgdat()

Hi Shi,

Sorry for the late reply. I hope it won't be too late.

NON-ACK by me, I think.

I noticed that your first has been merged. But it won't fix the problem
these code intended to fix.

After your patch 1, zone's spanned/present won't be set to 0 because:

free_area_init_node()
  |--> get_pfn_range_for_nid(&start_pfn, &end_pfn)
  |--> calculate_node_totalpages(pgdat, start_pfn, end_pfn, ...)
          | --> zone_spanned_pages_in_node()
                   | --> if (!node_start_pfn && !node_end_pfn) return 
0;    --------    false, won't return 0
          | --> zone_absent_pages_in_node()
                   | --> if (!node_start_pfn && !node_end_pfn) return 
0;    --------    false, won't return 0

This is caused by a little bug in your patch 1.

You should put memblock_add_node(start, size, nid) before 
hotadd_new_pgdat()
because:

hotadd_new_pgdat()
  | --> free_area_init_node()
           | --> get_pfn_range_for_nid()
                    | --> find memory ranges in memblock.

| --> memblock_add_node(start, size, nid) -------------------    if you 
add it here, it doesn't work.

The result will be like below if we hotadd node 5.
[ 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]


And also, if we merge this patch, /sys/devices/system/node/nodeX/meminfo 
will break.


Since this patch is not merged, I think let's just drop it.

And about the little bug in your patch 1, since I'm in a hurry, I have 
already send a patch to fix it.


Thanks. :)


On 08/11/2015 03:33 PM, Xishi Qiu wrote:
> After hotadd_new_pgdat()->free_area_init_node(), the pgdat and zone's spanned/present
> are both 0, so remove reset_node_managed_pages() and reset_node_managed_pages().
>
> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
> ---
>   mm/memory_hotplug.c | 25 -------------------------
>   1 file changed, 25 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 11f26cc..997dfad 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1065,16 +1065,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>   }
>   #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
>   
> -static void reset_node_present_pages(pg_data_t *pgdat)
> -{
> -	struct zone *z;
> -
> -	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
> -		z->present_pages = 0;
> -
> -	pgdat->node_present_pages = 0;
> -}
> -
>   /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
>   static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>   {
> @@ -1109,21 +1099,6 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>   	build_all_zonelists(pgdat, NULL);
>   	mutex_unlock(&zonelists_mutex);
>   
> -	/*
> -	 * zone->managed_pages is set to an approximate value in
> -	 * free_area_init_core(), which will cause
> -	 * /sys/device/system/node/nodeX/meminfo has wrong data.
> -	 * So reset it to 0 before any memory is onlined.
> -	 */
> -	reset_node_managed_pages(pgdat);
> -
> -	/*
> -	 * When memory is hot-added, all the memory is in offline state. So
> -	 * clear all zones' present_pages because they will be updated in
> -	 * online_pages() and offline_pages().
> -	 */
> -	reset_node_present_pages(pgdat);
> -
>   	return pgdat;
>   }
>   

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