On Mon, Aug 21, 2023 at 05:09:44AM +0100, Matthew Wilcox wrote:
> On Mon, Aug 21, 2023 at 12:46:20PM +0900, Byungchul Park wrote:
> > @@ -1219,6 +1220,9 @@ static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
> > /* How many times do we accept lock stealing from under a waiter? */
> > int sysctl_page_lock_unfairness = 5;
> >
> > +static struct dept_map __maybe_unused PG_locked_map = DEPT_MAP_INITIALIZER(PG_locked_map, NULL);
> > +static struct dept_map __maybe_unused PG_writeback_map = DEPT_MAP_INITIALIZER(PG_writeback_map, NULL);
>
> Hmm, why are these "maybe unused"? *digs*. Ah. Because
> sdt_might_sleep_start() becomes a no-op macro if DEPT is disabled.
>
> OK, the right way to handle this is
>
> #ifdef CONFIG_DEPT
> #define DEPT_MAP(name) static struct dept_map name = \
> DEPT_MAP_INITIALIZER(name, NULL)
> #else
> #define DEPT_MAP(name) /* */
> #endif
>
> And now DEPT takes up no space if disabled.
Currently:
#if !defined(CONFIG_DEPT)
struct dept_map { };
#endif
So I think it doesn't take space at all. Do you think I still need to
introduce e.g. DEPT_MAP()? Then I will. Thank you!
Byungchul
> /* */; is a somewhat unusual thing to see, but since this must work at
> top level, we can't use "do { } while (0)" like we usually do. Given
> where else this is likely to be used, i don't think it's going to be
> a problem ...
