linux-kernel - Re: [PATCH] memory-hotplug: Clear pgdat which is allocated by bootmem in try_offline

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Message-ID: <5447416C.5080106@jp.fujitsu.com>
Date:	Wed, 22 Oct 2014 14:32:28 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <zhenzhang.zhang@...wei.com>,
	<wangnan0@...wei.com>, <tangchen@...fujitsu.com>,
	<dave.hansen@...el.com>, <rientjes@...gle.com>
Subject: Re: [PATCH] memory-hotplug: Clear pgdat which is allocated by bootmem
 in try_offline_node()

(2014/10/22 1:56), Toshi Kani wrote:
> On Mon, 2014-10-20 at 19:05 +0900, Yasuaki Ishimatsu wrote:
>   :
>> When hot removing memory, pgdat is set to 0 in try_offline_node().
>> But if the pgdat is allocated by bootmem allocator, the clearing
>> step is skipped. And when hot adding the same memory, the uninitialized
>> pgdat is reused. But free_area_init_node() chacks wether pgdat is set
>

> s/chacks/checks

I'll update it.

>
>
>> to zero. As a result, free_area_init_node() hits WARN_ON().
>>
>> This patch clears pgdat which is allocated by bootmem allocator
>> in try_offline_node().
>>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>> CC: Zhang Zhen <zhenzhang.zhang@...wei.com>
>> CC: Wang Nan <wangnan0@...wei.com>
>> CC: Tang Chen <tangchen@...fujitsu.com>
>> CC: Toshi Kani <toshi.kani@...com>
>> CC: Dave Hansen <dave.hansen@...el.com>
>> CC: David Rientjes <rientjes@...gle.com>
>>
>> ---
>>   mm/memory_hotplug.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 29d8693..7649f7c 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1943,7 +1943,7 @@ void try_offline_node(int nid)
>>
>>   	if (!PageSlab(pgdat_page) && !PageCompound(pgdat_page))
>>   		/* node data is allocated from boot memory */
>> -		return;
>> +		goto out;
>

> Do we still need this if-statement?  That is, do we have to skip the
> for-loop below even though it checks with is_vmalloc_addr()?

You are right. The if-statement is not necessary. So the issue can be
fixed by just removing the if-statement.

I'll post updated patch soon.

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> -Toshi
>
>
>>   	/* free waittable in each zone */
>>   	for (i = 0; i < MAX_NR_ZONES; i++) {
>> @@ -1957,6 +1957,7 @@ void try_offline_node(int nid)
>>   			vfree(zone->wait_table);
>>   	}
>>
>> +out:
>>   	/*
>>   	 * Since there is no way to guarentee the address of pgdat/zone is not
>>   	 * on stack of any kernel threads or used by other kernel objects
>
>


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