Re: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup code

[Guoqing Jiang]

Hi Andrew,

On 5/19/20 9:35 AM, Guoqing Jiang wrote:
> On 5/19/20 7:12 AM, Andrew Morton wrote:
> > On Sun, 17 May 2020 23:47:18 +0200 Guoqing Jiang 
> > <guoqing.jiang@xxxxxxxxxxxxxxx> 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,
> > > ÂÂÂÂÂ if (rc != MIGRATEPAGE_SUCCESS)
> > > ÂÂÂÂÂÂÂÂÂ goto unlock_buffers;
> > > Â -ÂÂÂ ClearPagePrivate(page);
> > > -ÂÂÂ set_page_private(newpage, page_private(page));
> > > -ÂÂÂ set_page_private(page, 0);
> > > -ÂÂÂ put_page(page);
> > > +ÂÂÂ set_page_private(newpage, detach_page_private(page));
> > > ÂÂÂÂÂ get_page(newpage);
> > > Â ÂÂÂÂÂ 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]
> > Â #define set_page_private(page, v) ((page)->private = (v))
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ^
> > mm/migrate.c:800:2: note: in expansion of macro 'set_page_private'
> > ÂÂ set_page_private(newpage, detach_page_private(page));
> > ÂÂ ^~~~~~~~~~~~~~~~
> >
> > 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.

Only this patch missed the typecast. I guess I just need to send an 
updated patch
to replace this one (I am fine to send a new patch set if you want), 
sorry again for
the trouble.

> > 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)ÂÂÂÂÂÂÂÂÂÂÂÂ ((page)->private)
> -#define set_page_private(page, v)ÂÂÂÂÂ ((page)->private = (v))
> +static inline unsigned long page_private(struct page *page)
> +{
> +ÂÂÂÂÂÂ return page->private;
> +}
> +
> +static inline void set_page_private(struct page *page, unsigned long 
> priv_data)
> +{
> +ÂÂÂÂÂÂ page->private = priv_data;
> +}
>
> Then I get error like.
>
> fs/erofs/zdata.h: In function âz_erofs_onlinepage_indexâ:
> fs/erofs/zdata.h:126:8: error: lvalue required as unary â&â operand
> Â u.v = &page_private(page);
> ÂÂÂÂÂÂÂ ^
>
> I guess it is better to keep page_private as macro, please correct me 
> in case I
> missed something.

Lost of problems need to be fixed if change page_private to inline 
function, so I
think it is better to keep it and only convert set_page_private.

mm/compaction.c: In function âisolate_migratepages_blockâ:
./include/linux/compiler.h:287:20: error: lvalue required as unary â&â 
operand
ÂÂ __read_once_size(&(x), __u.__c, sizeof(x));Â \
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ^
./include/linux/compiler.h:293:22: note: in expansion of macro â__READ_ONCEâ
Â#define READ_ONCE(x) __READ_ONCE(x, 1)
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ^~~~~~~~~~~
mm/internal.h:293:34: note: in expansion of macro âREAD_ONCEâ
Â#define page_order_unsafe(page)Â READ_ONCE(page_private(page))


Thanks,
Guoqing