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Subject: Re: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup
 code
To:     Dave Chinner <david@fromorbit.com>
Cc:     akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        hch@infradead.org, willy@infradead.org
References: <20200517214718.468-1-guoqing.jiang@cloud.ionos.com>
 <20200517214718.468-11-guoqing.jiang@cloud.ionos.com>
 <20200521225220.GV2005@dread.disaster.area>
From:   Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Message-ID: <906f7469-492d-febc-c7ed-b01830ae900d@cloud.ionos.com>
Date:   Fri, 22 May 2020 09:18:25 +0200
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Hi Dave,

On 5/22/20 12:52 AM, Dave Chinner wrote:
> On Sun, May 17, 2020 at 11:47:18PM +0200, Guoqing Jiang wrote:
>> We can cleanup code a little by call detach_page_private here.
>>
>> Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
>> ---
>> No change since RFC V3.
>>
>>   mm/migrate.c | 5 +----
>>   1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/mm/migrate.c b/mm/migrate.c
>> index 5fed0305d2ec..f99502bc113c 100644
>> --- a/mm/migrate.c
>> +++ b/mm/migrate.c
>> @@ -804,10 +804,7 @@ static int __buffer_migrate_page(struct address_space *mapping,
>>   	if (rc != MIGRATEPAGE_SUCCESS)
>>   		goto unlock_buffers;
>>   
>> -	ClearPagePrivate(page);
>> -	set_page_private(newpage, page_private(page));
>> -	set_page_private(page, 0);
>> -	put_page(page);
>> +	set_page_private(newpage, detach_page_private(page));
> attach_page_private(newpage, detach_page_private(page));

Mattew had suggested it as follows, but not sure if we can reorder of 
the setup of
the bh and setting PagePrivate, so I didn't want to break the original 
syntax.

@@ -797,11 +797,7 @@ static int __buffer_migrate_page(struct address_space *mapping,
         if (rc != MIGRATEPAGE_SUCCESS)
                 goto unlock_buffers;
  
-       ClearPagePrivate(page);
-       set_page_private(newpage, page_private(page));
-       set_page_private(page, 0);
-       put_page(page);
-       get_page(newpage);
+       attach_page_private(newpage, detach_page_private(page));
  
         bh = head;
         do {
@@ -810,8 +806,6 @@ static int __buffer_migrate_page(struct address_space *mapping,
  
         } while (bh != head);
  
-       SetPagePrivate(newpage);
-
         if (mode != MIGRATE_SYNC_NO_COPY)


[1]. 
https://lore.kernel.org/lkml/20200502004158.GD29705@bombadil.infradead.org/
[2]. 
https://lore.kernel.org/lkml/e4d5ddc0-877f-6499-f697-2b7c0ddbf386@cloud.ionos.com/

Thanks,
Guoqing