void clear_bdi_congested(struct backing_dev_info *bdi, int rw);
void set_bdi_congested(struct backing_dev_info *bdi, int rw);
long congestion_wait(int rw, long timeout);
-void congestion_end(int rw);
#define bdi_cap_writeback_dirty(bdi) \
(!((bdi)->capabilities & BDI_CAP_NO_WRITEBACK))