Date:	Mon, 24 Aug 2015 17:39:50 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.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 08/24/2015 05:17 PM, Xishi Qiu wrote:
> 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?

Sorry, I didn't say it clearly since I was in a hurry.

If we move memblock_add_node() forward before hotadd_new_pgdat(),
then node_start_pfn and node_end_pfn won't be 0. And
zone_spanned_pages_in_node() and zone_absent_pages_in_node() won't
return 0.

In your patch, they will return 0. And that leads to the print problem.

>
>> 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.

Yes. I just found this bug in the log.

>
>> 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?

Yes.

>
>> [ 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?

No. There is no error output. But if you see 
/sys/devices/system/node/nodeX/meminfo,
memory size will double because totalpages is calculated once here, and 
one more time
when onlining memory.

I think reset it to 0 in add_memory() is just a temporary solution. Will 
improve it in the
future.

Thanks.

>
>> 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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