90  * Each wb (bdi_writeback) can perform writeback operations, is measured
92  * (bdi_writeback) is served by its embedded bdi->wb.
96  * memcg - blkcg combination can be served by its own wb by assigning a
97  * dedicated wb to each memcg, which enables isolation across different
101  * A cgroup wb is indexed on its bdi by the ID of the associated memcg,
104  * change as blkcg is disabled and enabled higher up in the hierarchy, a wb
106  * that a new wb for the combination can be created.
152 	struct percpu_ref refcnt;	/* used only for !root wb's */
187 	struct bdi_writeback wb;  /* the root writeback info for this bdi */  member
191 	struct mutex cgwb_release_mutex;  /* protect shutdown of wb structs */
226  * wb_tryget - try to increment a wb's refcount
227  * @wb: bdi_writeback to get
229 static inline bool wb_tryget(struct bdi_writeback *wb)  in wb_tryget()  argument
231 	if (wb != &wb->bdi->wb)  in wb_tryget()
232 		return percpu_ref_tryget(&wb->refcnt);  in wb_tryget()
237  * wb_get - increment a wb's refcount
238  * @wb: bdi_writeback to get
240 static inline void wb_get(struct bdi_writeback *wb)  in wb_get()  argument
242 	if (wb != &wb->bdi->wb)  in wb_get()
243 		percpu_ref_get(&wb->refcnt);  in wb_get()
247  * wb_put - decrement a wb's refcount
248  * @wb: bdi_writeback to put
250 static inline void wb_put(struct bdi_writeback *wb)  in wb_put()  argument
252 	if (WARN_ON_ONCE(!wb->bdi)) {  in wb_put()
260 	if (wb != &wb->bdi->wb)  in wb_put()
261 		percpu_ref_put(&wb->refcnt);  in wb_put()
265  * wb_dying - is a wb dying?
266  * @wb: bdi_writeback of interest
268  * Returns whether @wb is unlinked and being drained.
270 static inline bool wb_dying(struct bdi_writeback *wb)  in wb_dying()  argument
272 	return percpu_ref_is_dying(&wb->refcnt);  in wb_dying()
277 static inline bool wb_tryget(struct bdi_writeback *wb)  in wb_tryget()  argument
282 static inline void wb_get(struct bdi_writeback *wb)  in wb_get()  argument
286 static inline void wb_put(struct bdi_writeback *wb)  in wb_put()  argument
290 static inline bool wb_dying(struct bdi_writeback *wb)  in wb_dying()  argument