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Subject: Re: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup
 code
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, david@fromorbit.com,
        hch@infradead.org, willy@infradead.org
References: <20200517214718.468-1-guoqing.jiang@cloud.ionos.com>
 <20200517214718.468-11-guoqing.jiang@cloud.ionos.com>
 <20200518221235.1fa32c38e5766113f78e3f0d@linux-foundation.org>
From:   Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Message-ID: <aade5d75-c9e9-4021-6eb7-174a921a7958@cloud.ionos.com>
Date:   Tue, 19 May 2020 09:35:59 +0200
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On 5/19/20 7:12 AM, Andrew Morton wrote:
> On Sun, 17 May 2020 23:47:18 +0200 Guoqing Jiang <guoqing.jiang@cloud.ionos.com> wrote:
>
>> We can cleanup code a little by call detach_page_private here.
>>
>> ...
>>
>> --- 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));
>>   	get_page(newpage);
>>   
>>   	bh = head;
> mm/migrate.c: In function '__buffer_migrate_page':
> ./include/linux/mm_types.h:243:52: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
>   #define set_page_private(page, v) ((page)->private = (v))
>                                                      ^
> mm/migrate.c:800:2: note: in expansion of macro 'set_page_private'
>    set_page_private(newpage, detach_page_private(page));
>    ^~~~~~~~~~~~~~~~
>
> The fact that set_page_private(detach_page_private()) generates a type
> mismatch warning seems deeply wrong, surely.
>
> Please let's get the types sorted out - either unsigned long or void *,
> not half-one and half-the other.  Whatever needs the least typecasting
> at callsites, I suggest.

Sorry about that, I should notice the warning before. I will double 
check if other
places need the typecast or not, then send a new version.

> And can we please implement set_page_private() and page_private() with
> inlined C code?  There is no need for these to be macros.

Just did a quick change.

-#define page_private(page)             ((page)->private)
-#define set_page_private(page, v)      ((page)->private = (v))
+static inline unsigned long page_private(struct page *page)
+{
+       return page->private;
+}
+
+static inline void set_page_private(struct page *page, unsigned long 
priv_data)
+{
+       page->private = priv_data;
+}

Then I get error like.

fs/erofs/zdata.h: In function ‘z_erofs_onlinepage_index’:
fs/erofs/zdata.h:126:8: error: lvalue required as unary ‘&’ operand
   u.v = &page_private(page);
         ^

I guess it is better to keep page_private as macro, please correct me in 
case I
missed something.

Thanks,
Guoqing