linux-kernel - Re: [PATCH 2/2] x86,mem-hotplug: modify PGD entry when removing memory

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Date:	Tue, 24 Jun 2014 09:31:50 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	<akpm@...ux-foundation.org>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <hpa@...or.com>, <tangchen@...fujitsu.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<x86@...nel.org>, <guz.fnst@...fujitsu.com>,
	<zhangyanfei@...fujitsu.com>
Subject: Re: [PATCH 2/2] x86,mem-hotplug: modify PGD entry when removing memory

(2014/06/21 3:30), Toshi Kani wrote:
> On Wed, 2014-06-18 at 15:38 +0900, Yasuaki Ishimatsu wrote:
>   :
>> @@ -186,7 +186,12 @@ void sync_global_pgds(unsigned long start, unsigned long end)
>>   		const pgd_t *pgd_ref = pgd_offset_k(address);
>>   		struct page *page;
>>
>> -		if (pgd_none(*pgd_ref))
>> +		/*
>> +		 * When it is called after memory hot remove, pgd_none()
>> +		 * returns true. In this case (removed == 1), we must clear
>> +		 * the PGD entries in the local PGD level page.
>> +		 */
>> +		if (pgd_none(*pgd_ref) && !removed)
>>   			continue;
>>
>>   		spin_lock(&pgd_lock);
>> @@ -199,12 +204,18 @@ void sync_global_pgds(unsigned long start, unsigned long end)
>>   			pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
>>   			spin_lock(pgt_lock);
>>
>> -			if (pgd_none(*pgd))
>> -				set_pgd(pgd, *pgd_ref);
>> -			else

>> +			if (!pgd_none(*pgd_ref) && !pgd_none(*pgd))
>>   				BUG_ON(pgd_page_vaddr(*pgd)
>>   				       != pgd_page_vaddr(*pgd_ref));
>>
>> +			if (removed) {
>
> Shouldn't this condition be "else if"?

The first if sentence checks whether PGDs hit to BUG_ON. And the second
if sentence checks whether the function was called after hot-removing memory.
I think that the first if sentence and the second if sentence check different
things. So I think the condition should be "if" sentence.

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> -Toshi
>
>> +				if (pgd_none(*pgd_ref) && !pgd_none(*pgd))
>> +					pgd_clear(pgd);
>> +			} else {
>> +				if (pgd_none(*pgd))
>> +					set_pgd(pgd, *pgd_ref);
>> +			}
>> +
>>   			spin_unlock(pgt_lock);
>>   		}
>
>


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