[PATCH 08/13] writeback: add support to collect stats for all writeback ctxs

[Kundan Kumar <kundan.kumar@xxxxxxxxxxx>]

Modified stats collection to collect stats for all the writeback
contexts within a bdi.

Signed-off-by: Kundan Kumar <kundan.kumar@xxxxxxxxxxx>
Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
---
 mm/backing-dev.c | 72 ++++++++++++++++++++++++++++--------------------
 1 file changed, 42 insertions(+), 30 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 5479e2d34160..d416122e2914 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -50,6 +50,7 @@ struct wb_stats {
 	unsigned long nr_written;
 	unsigned long dirty_thresh;
 	unsigned long wb_thresh;
+	unsigned long state;
 };
 
 static struct dentry *bdi_debug_root;
@@ -81,6 +82,7 @@ static void collect_wb_stats(struct wb_stats *stats,
 	stats->nr_dirtied += wb_stat(wb, WB_DIRTIED);
 	stats->nr_written += wb_stat(wb, WB_WRITTEN);
 	stats->wb_thresh += wb_calc_thresh(wb, stats->dirty_thresh);
+	stats->state |= wb->state;
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
@@ -89,22 +91,27 @@ static void bdi_collect_stats(struct backing_dev_info *bdi,
 			      struct wb_stats *stats)
 {
 	struct bdi_writeback *wb;
+	struct bdi_writeback_ctx *bdi_wb_ctx;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(wb, &bdi->wb_ctx_arr[0]->wb_list, bdi_node) {
-		if (!wb_tryget(wb))
-			continue;
+	for_each_bdi_wb_ctx(bdi, bdi_wb_ctx)
+		list_for_each_entry_rcu(wb, &bdi_wb_ctx->wb_list, bdi_node) {
+			if (!wb_tryget(wb))
+				continue;
 
-		collect_wb_stats(stats, wb);
-		wb_put(wb);
-	}
+			collect_wb_stats(stats, wb);
+			wb_put(wb);
+		}
 	rcu_read_unlock();
 }
 #else
 static void bdi_collect_stats(struct backing_dev_info *bdi,
 			      struct wb_stats *stats)
 {
-	collect_wb_stats(stats, &bdi->wb_ctx_arr[0]->wb);
+	struct bdi_writeback_ctx *bdi_wb_ctx;
+
+	for_each_bdi_wb_ctx(bdi, bdi_wb_ctx)
+		collect_wb_stats(stats, &bdi_wb_ctx->wb);
 }
 #endif
 
@@ -150,7 +157,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 		   stats.nr_io,
 		   stats.nr_more_io,
 		   stats.nr_dirty_time,
-		   !list_empty(&bdi->bdi_list), bdi->wb_ctx_arr[0]->wb.state);
+		   !list_empty(&bdi->bdi_list), stats.state);
 
 	return 0;
 }
@@ -195,35 +202,40 @@ static int cgwb_debug_stats_show(struct seq_file *m, void *v)
 {
 	struct backing_dev_info *bdi = m->private;
 	struct bdi_writeback *wb;
+	struct bdi_writeback_ctx *bdi_wb_ctx;
 	unsigned long background_thresh;
 	unsigned long dirty_thresh;
+	struct wb_stats stats;
 
 	global_dirty_limits(&background_thresh, &dirty_thresh);
+	stats.dirty_thresh = dirty_thresh;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(wb, &bdi->wb_ctx_arr[0]->wb_list, bdi_node) {
-		struct wb_stats stats = { .dirty_thresh = dirty_thresh };
-
-		if (!wb_tryget(wb))
-			continue;
-
-		collect_wb_stats(&stats, wb);
-
-		/*
-		 * Calculate thresh of wb in writeback cgroup which is min of
-		 * thresh in global domain and thresh in cgroup domain. Drop
-		 * rcu lock because cgwb_calc_thresh may sleep in
-		 * cgroup_rstat_flush. We can do so here because we have a ref.
-		 */
-		if (mem_cgroup_wb_domain(wb)) {
-			rcu_read_unlock();
-			stats.wb_thresh = min(stats.wb_thresh, cgwb_calc_thresh(wb));
-			rcu_read_lock();
+	for_each_bdi_wb_ctx(bdi, bdi_wb_ctx) {
+		list_for_each_entry_rcu(wb, &bdi_wb_ctx->wb_list, bdi_node) {
+			if (!wb_tryget(wb))
+				continue;
+
+			collect_wb_stats(&stats, wb);
+
+			/*
+			 * Calculate thresh of wb in writeback cgroup which is
+			 * min of thresh in global domain and thresh in cgroup
+			 * domain. Drop rcu lock because cgwb_calc_thresh may
+			 * sleep in cgroup_rstat_flush. We can do so here
+			 * because we have a ref.
+			 */
+			if (mem_cgroup_wb_domain(wb)) {
+				rcu_read_unlock();
+				stats.wb_thresh = min(stats.wb_thresh,
+						      cgwb_calc_thresh(wb));
+				rcu_read_lock();
+			}
+
+			wb_stats_show(m, wb, &stats);
+
+			wb_put(wb);
 		}
-
-		wb_stats_show(m, wb, &stats);
-
-		wb_put(wb);
 	}
 	rcu_read_unlock();
 
-- 
2.25.1