writeback: make congestion functions per bdi_writeback

Currently, all congestion functions take bdi (backing_dev_info) and
always operate on the root wb (bdi->wb) and the congestion state from
the block layer is propagated only for the root blkcg.  This patch
introduces {set|clear}_wb_congested() and wb_congested() which take a
bdi_writeback_congested and bdi_writeback respectively.  The bdi
counteparts are now wrappers invoking the wb based functions on
@bdi->wb.

While converting clear_bdi_congested() to clear_wb_congested(), the
local variable declaration order between @wqh and @bit is swapped for
cosmetic reason.

This patch just adds the new wb based functions.  The following
patches will apply them.

v2: Updated for bdi_writeback_congested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/backing-dev-defs.h

@@ -163,7 +163,17 @@ enum {
 	BLK_RW_SYNC	= 1,
 };
 
-void clear_bdi_congested(struct backing_dev_info *bdi, int sync);
-void set_bdi_congested(struct backing_dev_info *bdi, int sync);
+void clear_wb_congested(struct bdi_writeback_congested *congested, int sync);
+void set_wb_congested(struct bdi_writeback_congested *congested, int sync);
+
+static inline void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
+{
+	clear_wb_congested(bdi->wb.congested, sync);
+}
+
+static inline void set_bdi_congested(struct backing_dev_info *bdi, int sync)
+{
+	set_wb_congested(bdi->wb.congested, sync);
+}
 
 #endif	/* __LINUX_BACKING_DEV_DEFS_H */

include/linux/backing-dev.h

@@ -167,27 +167,13 @@ static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
 	return sb->s_bdi;
 }
 
-static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
+static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
 {
+	struct backing_dev_info *bdi = wb->bdi;
+
 	if (bdi->congested_fn)
-		return bdi->congested_fn(bdi->congested_data, bdi_bits);
-	return (bdi->wb.congested->state & bdi_bits);
-}
-
-static inline int bdi_read_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, 1 << WB_sync_congested);
-}
-
-static inline int bdi_write_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, 1 << WB_async_congested);
-}
-
-static inline int bdi_rw_congested(struct backing_dev_info *bdi)
-{
-	return bdi_congested(bdi, (1 << WB_sync_congested) |
-				  (1 << WB_async_congested));
+		return bdi->congested_fn(bdi->congested_data, cong_bits);
+	return wb->congested->state & cong_bits;
 }
 
 long congestion_wait(int sync, long timeout);
@@ -454,4 +440,25 @@ static inline void wb_blkcg_offline(struct blkcg *blkcg)
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 
+static inline int bdi_congested(struct backing_dev_info *bdi, int cong_bits)
+{
+	return wb_congested(&bdi->wb, cong_bits);
+}
+
+static inline int bdi_read_congested(struct backing_dev_info *bdi)
+{
+	return bdi_congested(bdi, 1 << WB_sync_congested);
+}
+
+static inline int bdi_write_congested(struct backing_dev_info *bdi)
+{
+	return bdi_congested(bdi, 1 << WB_async_congested);
+}
+
+static inline int bdi_rw_congested(struct backing_dev_info *bdi)
+{
+	return bdi_congested(bdi, (1 << WB_sync_congested) |
+				  (1 << WB_async_congested));
+}
+
 #endif	/* _LINUX_BACKING_DEV_H */

mm/backing-dev.c

@@ -896,31 +896,31 @@ static wait_queue_head_t congestion_wqh[2] = {
 		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 	};
-static atomic_t nr_bdi_congested[2];
+static atomic_t nr_wb_congested[2];
 
-void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
+void clear_wb_congested(struct bdi_writeback_congested *congested, int sync)
 {
-	enum wb_state bit;
 	wait_queue_head_t *wqh = &congestion_wqh[sync];
+	enum wb_state bit;
 
 	bit = sync ? WB_sync_congested : WB_async_congested;
-	if (test_and_clear_bit(bit, &bdi->wb.congested->state))
-		atomic_dec(&nr_bdi_congested[sync]);
+	if (test_and_clear_bit(bit, &congested->state))
+		atomic_dec(&nr_wb_congested[sync]);
 	smp_mb__after_atomic();
 	if (waitqueue_active(wqh))
 		wake_up(wqh);
 }
-EXPORT_SYMBOL(clear_bdi_congested);
+EXPORT_SYMBOL(clear_wb_congested);
 
-void set_bdi_congested(struct backing_dev_info *bdi, int sync)
+void set_wb_congested(struct bdi_writeback_congested *congested, int sync)
 {
 	enum wb_state bit;
 
 	bit = sync ? WB_sync_congested : WB_async_congested;
-	if (!test_and_set_bit(bit, &bdi->wb.congested->state))
-		atomic_inc(&nr_bdi_congested[sync]);
+	if (!test_and_set_bit(bit, &congested->state))
+		atomic_inc(&nr_wb_congested[sync]);
 }
-EXPORT_SYMBOL(set_bdi_congested);
+EXPORT_SYMBOL(set_wb_congested);
 
 /**
  * congestion_wait - wait for a backing_dev to become uncongested
@@ -979,7 +979,7 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout)
 	 * encountered in the current zone, yield if necessary instead
 	 * of sleeping on the congestion queue
 	 */
-	if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
+	if (atomic_read(&nr_wb_congested[sync]) == 0 ||
 	    !test_bit(ZONE_CONGESTED, &zone->flags)) {
 		cond_resched();