linux-kernel - Re: [PATCH v2 3/3] KVM: remove dummy pages

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Date:	Thu, 26 Jul 2012 17:25:07 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] KVM: remove dummy pages

On 07/26/2012 04:56 PM, Avi Kivity wrote:
> On 07/26/2012 06:58 AM, Xiao Guangrong wrote:
>> Currently, kvm allocates some pages and use them as error indicators,
>> it wastes memory and is not good for scalability
>>
>> Base on Avi's suggestion, we use the error codes instead of these pages
>> to indicate the error conditions
>>
>>
>> +static pfn_t get_bad_pfn(void)
>> +{
>> +	return -ENOENT;
>> +}
>> +
>> +pfn_t get_fault_pfn(void)
>> +{
>> +	return -EFAULT;
>> +}
>> +EXPORT_SYMBOL_GPL(get_fault_pfn);
>> +
>> +static pfn_t get_hwpoison_pfn(void)
>> +{
>> +	return -EHWPOISON;
>> +}
>> +
> 
> Would be better as #defines

Okay.

> 
>>  int is_hwpoison_pfn(pfn_t pfn)
>>  {
>> -	return pfn == hwpoison_pfn;
>> +	return pfn == -EHWPOISON;
>>  }
>>  EXPORT_SYMBOL_GPL(is_hwpoison_pfn);
>>
>>  int is_noslot_pfn(pfn_t pfn)
>>  {
>> -	return pfn == bad_pfn;
>> +	return pfn == -ENOENT;
>>  }
>>  EXPORT_SYMBOL_GPL(is_noslot_pfn);
>>
>>  int is_invalid_pfn(pfn_t pfn)
>>  {
>> -	return pfn == hwpoison_pfn || pfn == fault_pfn;
>> +	return !is_noslot_pfn(pfn) && is_error_pfn(pfn);
>>  }
>>  EXPORT_SYMBOL_GPL(is_invalid_pfn);
>>
> 
> So is_*_pfn() could go away and be replaced by ==.
> 

Okay.

>>
>>  EXPORT_SYMBOL_GPL(gfn_to_page);
>>
>>  void kvm_release_page_clean(struct page *page)
>>  {
>> -	kvm_release_pfn_clean(page_to_pfn(page));
>> +	if (!is_error_page(page))
>> +		kvm_release_pfn_clean(page_to_pfn(page));
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_release_page_clean);
> 
> Note, we can remove calls to kvm_release_page_clean() from error paths
> now, so in the future we can drop the test.
> 

Right, since the release path (kvm_release_page_clean) is used in many place
and on many architectures, i did the change as small as possible for good
review.

> Since my comments are better done as a separate patch, 

Yes, i will make a patch to apply all your comments. Thank you, Avi!

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