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

[Xishi Qiu]

On 2015/8/24 17:39, Tang Chen wrote:

> 
> 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.
> 

Hi Tang,

Do you mean si_meminfo_node() -> val->totalram = managed_pages; will be added double?
But my patch will keep it 0 in hotadd_new_pgdat(), so it will not be double, right?

Thanks,
Xishi Qiu

> 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@xxxxxxxxxx>
>>>> ---
>>>>    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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