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.
/* */; 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 ...
