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:	Mon, 24 Aug 2015 17:17:07 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Tang Chen <tangchen@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	<izumi.taku@...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()

On 2015/8/23 18:28, Tang Chen wrote:

> 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
> 

Hi Tang,

Thank you for your reply. When we add a new node, it is not included in the
memblock, I have no idea why zone_spanned_pages_in_node() and zone_absent_pages_in_node()
won't return 0. Do you add some debug code and print it?

> 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:
> 

My patch is just add an empty node first, later __add_zone() will update the size.
But it is all right put here, and it can fix the print bug.

> 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]

	pr_info("Initmem setup node %d [mem %#018Lx-%#018Lx]\n", nid,
		(u64)start_pfn << PAGE_SHIFT, ((u64)end_pfn << PAGE_SHIFT) - 1);
start_pfn and end_pfn are both 0, and 0-1 -> 0xffffffffffffffff, right?

> [ 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.
> 

trigger call trace?

> 
> 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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