linux-kernel - Re: [PATCH x86,mm] fix pgt_buf

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Message-ID: <4E797B55.20102@cn.fujitsu.com>
Date:	Wed, 21 Sep 2011 13:51:17 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Tejun Heo <tj@...nel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Stephen Wilson <wilsons@...rt.ca>
Subject: Re: [PATCH x86,mm]  fix pgt_buf_end when memory hotplug

On 09/08/2011 11:21 PM, Stefano Stabellini wrote:
> On Thu, 8 Sep 2011, Lai Jiangshan wrote:
>>
>> When I test memory hotplug, such message is always outputted when hot-adding
>> a memory block:
>>
>> initial kernel pagetable allocation wasted ffffffffffffffff pages
> 
> I take you are using tip/x86/mm, because that is the only branch that
> contains that warning.

No,
I was using tip/master.

Thanks,
Lai

> 
> 
>> This message comes from init_memory_mapping(), it shows "pgt_buf_end" is
>> incorrect here, and I found it was caused by alloc_low_page().
>>
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>> ---
>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>> index bbaaa00..e138e0a 100644
>> --- a/arch/x86/mm/init_64.c
>> +++ b/arch/x86/mm/init_64.c
>> @@ -317,7 +317,7 @@ void __init cleanup_highmap(void)
>>  
>>  static __ref void *alloc_low_page(unsigned long *phys)
>>  {
>> -	unsigned long pfn = pgt_buf_end++;
>> +	unsigned long pfn;
>>  	void *adr;
>>  
>>  	if (after_bootmem) {
>> @@ -327,6 +327,7 @@ static __ref void *alloc_low_page(unsigned long *phys)
>>  		return adr;
>>  	}
>>  
>> +	pfn = pgt_buf_end++;
>>  	if (pfn >= pgt_buf_top)
>>  		panic("alloc_low_page: ran out of memory");
> 
> 
> This patch makes sense to me. It would also make sense to print the
> "allocation wasted" warning only if (!after_bootmem).
> --
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