On 5/19/20 7:12 AM, Andrew Morton wrote:

On Sun, 17 May 2020 23:47:18 +0200 Guoqing Jiang [off-list ref] wrote:

quoted

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