Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is migrated

[Hugh Dickins]

On Tue, 27 Nov 2018, Mike Rapoport wrote:
> On Mon, Nov 26, 2018 at 11:27:07AM -0800, Hugh Dickins wrote:
> > 
> > +/*
> > + * A choice of three behaviors for wait_on_page_bit_common():
> > + */
> > +enum behavior {
> > +	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
> > +			 * __lock_page() waiting on then setting PG_locked.
> > +			 */
> > +	SHARED,		/* Hold ref to page and check the bit when woken, like
> > +			 * wait_on_page_writeback() waiting on PG_writeback.
> > +			 */
> > +	DROP,		/* Drop ref to page before wait, no check when woken,
> > +			 * like put_and_wait_on_page_locked() on PG_locked.
> > +			 */
> > +};
> 
> Can we please make it:
> 
> /**
>  * enum behavior - a choice of three behaviors for wait_on_page_bit_common()
>  */
> enum behavior {
> 	/**
> 	 * @EXCLUSIVE: Hold ref to page and take the bit when woken,
> 	 * like __lock_page() waiting on then setting %PG_locked.
> 	 */
> 	EXCLUSIVE,
> 	/**
> 	 * @SHARED: Hold ref to page and check the bit when woken,
> 	 * like wait_on_page_writeback() waiting on %PG_writeback.
> 	 */
> 	SHARED,
> 	/**
> 	 * @DROP: Drop ref to page before wait, no check when woken,
> 	 * like put_and_wait_on_page_locked() on %PG_locked.
> 	 */
> 	DROP,
> };

I'm with Matthew, I'd prefer not: the first looks a more readable,
less cluttered comment to me than the second: this is just an arg
to an internal helper in mm/filemap.c, itself not kernel-doc'ed.

But the comment is not there for me: if consensus is that the
second is preferable, then sure, we can change it over.

Hugh