linux-kernel - Re: [PATCH 2/2] mm/migrate_device: further convert migrate_device

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Date: Wed, 14 Feb 2024 15:10:20 -0800
From: Sidhartha Kumar <sidhartha.kumar@...cle.com>
To: Alistair Popple <apopple@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, willy@...radead.org
Subject: Re: [PATCH 2/2] mm/migrate_device: further convert
 migrate_device_finalize() to folios

On 2/14/24 2:45 PM, Alistair Popple wrote:
> 
> Sidhartha Kumar <sidhartha.kumar@...cle.com> writes:
> 
>> Use folio api functions from the already defined src and dst folio
>> variables.
>>
>> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
>> ---
>>   mm/migrate_device.c | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
>> index 9152a329b0a68..a48d5cdb28553 100644
>> --- a/mm/migrate_device.c
>> +++ b/mm/migrate_device.c
>> @@ -843,17 +843,17 @@ void migrate_device_finalize(unsigned long *src_pfns,
>>   		remove_migration_ptes(src, dst, false);
>>   		folio_unlock(src);
>>   
>> -		if (is_zone_device_page(page))
>> -			put_page(page);
>> +		if (folio_is_zone_device(src))
>> +			folio_put(src);
>>   		else
>> -			putback_lru_page(page);
>> +			folio_putback_lru(src);
>>   
>>   		if (newpage != page) {
>> -			unlock_page(newpage);
>> -			if (is_zone_device_page(newpage))
>> -				put_page(newpage);
> 
> Defining migrate_pfn_to_folio() would also allow the removal of the
> newpage and page variables entirely which I think would make this
> clearer.
> 
> As an aside is there any motivation for making these changes other than
> as a general cleanup? I ask only because I have been looking at allowing
> device pages with order > 0 so have some of these clean-ups in a local
> tree as they're a pre-requisite for that.
> 
>   - Alistair
> 

Hello,

The motivation is just general cleanup. In folio-compat.c I saw that 
putback_lru_page() does not have much users left so I could convert them and 
then just get rid of putback_lru_page(). Should I still continue with a v2 that 
will include defining a migrate_pfn_to_folio() or wait for your clean-ups?

Thanks,
Sid

>> +			folio_unlock(dst);
>> +			if (folio_is_zone_device(dst))
>> +				folio_put(dst);
>>   			else
>> -				putback_lru_page(newpage);
>> +				folio_putback_lru(dst);
>>   		}
>>   	}
>>   }
>