linux-kernel - Re: [PATCH 10/10] mm/migrate.c: call detach_page

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Date:   Sun, 24 May 2020 21:02:10 +0200
From:   Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dave Chinner <david@...morbit.com>, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        hch@...radead.org, willy@...radead.org
Subject: Re: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup
 code

On 5/23/20 1:53 AM, Andrew Morton wrote:
> On Fri, 22 May 2020 09:18:25 +0200 Guoqing Jiang <guoqing.jiang@...ud.ionos.com> wrote:
>
>>>> -	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)
> This is OK - coherency between PG_private and the page's buffer
> ring is maintained by holding lock_page().

Appreciate for your explanation.

Thanks,
Guoqing

> I have (effectively) applied the above change.