[v2,1/2] mm/page_alloc: drop the unnecessary pfn_valid() for start pfn

Commit Message

Baolin Wang April 23, 2023, 10:59 a.m. UTC

We've already used pfn_to_online_page() for start pfn to make sure
it is online and valid, so the pfn_valid() for the start pfn is
unnecessary, drop it.

Signed-off-by: Baolin Wang <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Reviewed-by: "Huang, Ying" <[e-mail]>
---
Changes from v1:
 - Collect reviewed tags. Thanks David and Ying.
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Michal Hocko April 24, 2023, 9:50 a.m. UTC | #1

On Sun 23-04-23 18:59:10, Baolin Wang wrote:
> We've already used pfn_to_online_page() for start pfn to make sure

Who is we? I do not see any note explicitly requiring that start_pfn has
to be valid for __pageblock_pfn_to_page.

> it is online and valid, so the pfn_valid() for the start pfn is
> unnecessary, drop it.
> 
> Signed-off-by: Baolin Wang <[e-mail]>
> Reviewed-by: David Hildenbrand <[e-mail]>
> Reviewed-by: "Huang, Ying" <[e-mail]>
> ---
> Changes from v1:
>  - Collect reviewed tags. Thanks David and Ying.
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9de2a18519a1..6457b64fe562 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>  	/* end_pfn is one past the range we are checking */
>  	end_pfn--;
>  
> -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
> +	if (!pfn_valid(end_pfn))
>  		return NULL;
>  
>  	start_page = pfn_to_online_page(start_pfn);
> -- 
> 2.27.0

Baolin Wang April 24, 2023, 10:46 a.m. UTC | #2

On 4/24/2023 5:50 PM, Michal Hocko wrote:
> On Sun 23-04-23 18:59:10, Baolin Wang wrote:
>> We've already used pfn_to_online_page() for start pfn to make sure
> 
> Who is we? I do not see any note explicitly requiring that start_pfn has
> to be valid for __pageblock_pfn_to_page.

Sorry for confusing, what I mean is the __pageblock_pfn_to_page() 
function, which has used pfn_to_online_page() for start pfn. So the 
pfn_valid() in __pageblock_pfn_to_page() for start pfn is unnecessary.

I will update the commit log to make it clear.

>> it is online and valid, so the pfn_valid() for the start pfn is
>> unnecessary, drop it.
>>
>> Signed-off-by: Baolin Wang <[e-mail]>
>> Reviewed-by: David Hildenbrand <[e-mail]>
>> Reviewed-by: "Huang, Ying" <[e-mail]>
>> ---
>> Changes from v1:
>>   - Collect reviewed tags. Thanks David and Ying.
>> ---
>>   mm/page_alloc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9de2a18519a1..6457b64fe562 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>>   	/* end_pfn is one past the range we are checking */
>>   	end_pfn--;
>>   
>> -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
>> +	if (!pfn_valid(end_pfn))
>>   		return NULL;
>>   
>>   	start_page = pfn_to_online_page(start_pfn);
>> -- 
>> 2.27.0
>

Michal Hocko April 24, 2023, 10:54 a.m. UTC | #3

On Mon 24-04-23 18:46:40, Baolin Wang wrote:
> 
> 
> On 4/24/2023 5:50 PM, Michal Hocko wrote:
> > On Sun 23-04-23 18:59:10, Baolin Wang wrote:
> > > We've already used pfn_to_online_page() for start pfn to make sure
> > 
> > Who is we? I do not see any note explicitly requiring that start_pfn has
> > to be valid for __pageblock_pfn_to_page.
> 
> Sorry for confusing, what I mean is the __pageblock_pfn_to_page() function,
> which has used pfn_to_online_page() for start pfn. So the pfn_valid() in
> __pageblock_pfn_to_page() for start pfn is unnecessary.
> 
> I will update the commit log to make it clear.

Your comment suggested that the check _has_ already been done. Which is
not the case. pfn_to_online_page is called later in the function so I
guess you should rephrase as following:

"
__pageblock_pfn_to_page currently performs both pfn_valid check and
pfn_to_online_page. The former one is redundant because the latter is a
stronger check. Drop pfn_valid.
"

With that or something going along with that. Feel free to add
Acked-by: Michal Hocko <[e-mail]>

> > > it is online and valid, so the pfn_valid() for the start pfn is
> > > unnecessary, drop it.
> > > 
> > > Signed-off-by: Baolin Wang <[e-mail]>
> > > Reviewed-by: David Hildenbrand <[e-mail]>
> > > Reviewed-by: "Huang, Ying" <[e-mail]>
> > > ---
> > > Changes from v1:
> > >   - Collect reviewed tags. Thanks David and Ying.
> > > ---
> > >   mm/page_alloc.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 9de2a18519a1..6457b64fe562 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
> > >   	/* end_pfn is one past the range we are checking */
> > >   	end_pfn--;
> > > -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
> > > +	if (!pfn_valid(end_pfn))
> > >   		return NULL;
> > >   	start_page = pfn_to_online_page(start_pfn);
> > > -- 
> > > 2.27.0
> >

Baolin Wang April 24, 2023, 11:21 a.m. UTC | #4

On 4/24/2023 6:54 PM, Michal Hocko wrote:
> On Mon 24-04-23 18:46:40, Baolin Wang wrote:
>>
>>
>> On 4/24/2023 5:50 PM, Michal Hocko wrote:
>>> On Sun 23-04-23 18:59:10, Baolin Wang wrote:
>>>> We've already used pfn_to_online_page() for start pfn to make sure
>>>
>>> Who is we? I do not see any note explicitly requiring that start_pfn has
>>> to be valid for __pageblock_pfn_to_page.
>>
>> Sorry for confusing, what I mean is the __pageblock_pfn_to_page() function,
>> which has used pfn_to_online_page() for start pfn. So the pfn_valid() in
>> __pageblock_pfn_to_page() for start pfn is unnecessary.
>>
>> I will update the commit log to make it clear.
> 
> Your comment suggested that the check _has_ already been done. Which is
> not the case. pfn_to_online_page is called later in the function so I
> guess you should rephrase as following:
> 
> "
> __pageblock_pfn_to_page currently performs both pfn_valid check and
> pfn_to_online_page. The former one is redundant because the latter is a
> stronger check. Drop pfn_valid.
> "

Yes, will change the commit log.

> 
> With that or something going along with that. Feel free to add
> Acked-by: Michal Hocko <[e-mail]>

Thanks.

>>>> it is online and valid, so the pfn_valid() for the start pfn is
>>>> unnecessary, drop it.
>>>>
>>>> Signed-off-by: Baolin Wang <[e-mail]>
>>>> Reviewed-by: David Hildenbrand <[e-mail]>
>>>> Reviewed-by: "Huang, Ying" <[e-mail]>
>>>> ---
>>>> Changes from v1:
>>>>    - Collect reviewed tags. Thanks David and Ying.
>>>> ---
>>>>    mm/page_alloc.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index 9de2a18519a1..6457b64fe562 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -1512,7 +1512,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
>>>>    	/* end_pfn is one past the range we are checking */
>>>>    	end_pfn--;
>>>> -	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
>>>> +	if (!pfn_valid(end_pfn))
>>>>    		return NULL;
>>>>    	start_page = pfn_to_online_page(start_pfn);
>>>> -- 
>>>> 2.27.0
>>>
>

Patch

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9de2a18519a1..6457b64fe562 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1512,7 +1512,7 @@  struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
 	/* end_pfn is one past the range we are checking */
 	end_pfn--;
 
-	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
+	if (!pfn_valid(end_pfn))
 		return NULL;
 
 	start_page = pfn_to_online_page(start_pfn);