[PATCH v6 3/3] writeback: record bdev targets in foreign writeback tracepoints

[Julian Sun <sunjunchao@bytedance.com>]

Add dev to track_foreign_dirty and flush_foreign so traces can
distinguish foreign-wb tracking from the bdev-only path. Append the
field to each event and print it as major:minor; zero denotes the
normal foreign-wb path.

Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
---
 include/trace/events/writeback.h | 22 ++++++++++++++--------
 mm/memcontrol.c                  |  9 ++++++---
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 13ee076ccd16..ffd1b8df4231 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -273,9 +273,9 @@ TRACE_EVENT(inode_switch_wbs,
 
 TRACE_EVENT(track_foreign_dirty,
 
-	TP_PROTO(struct folio *folio, struct bdi_writeback *wb),
+	TP_PROTO(struct folio *folio, struct bdi_writeback *wb, dev_t dev),
 
-	TP_ARGS(folio, wb),
+	TP_ARGS(folio, wb, dev),
 
 	TP_STRUCT__entry(
 		__array(char,		name, 32)
@@ -284,6 +284,7 @@ TRACE_EVENT(track_foreign_dirty,
 		__field(u64,		cgroup_ino)
 		__field(u64,		page_cgroup_ino)
 		__field(unsigned int,	memcg_id)
+		__field(dev_t,		dev)
 	),
 
 	TP_fast_assign(
@@ -295,34 +296,37 @@ TRACE_EVENT(track_foreign_dirty,
 		__entry->ino		= inode ? inode->i_ino : 0;
 		__entry->memcg_id	= wb->memcg_css->id;
 		__entry->cgroup_ino	= __trace_wb_assign_cgroup(wb);
+		__entry->dev		= dev;
 
 		rcu_read_lock();
 		__entry->page_cgroup_ino = cgroup_ino(folio_memcg(folio)->css.cgroup);
 		rcu_read_unlock();
 	),
 
-	TP_printk("bdi %s[%llu]: ino=%llu memcg_id=%u cgroup_ino=%llu page_cgroup_ino=%llu",
+	TP_printk("bdi %s[%llu]: ino=%llu memcg_id=%u cgroup_ino=%llu page_cgroup_ino=%llu dev=%u:%u",
 		__entry->name,
 		__entry->bdi_id,
 		__entry->ino,
 		__entry->memcg_id,
 		__entry->cgroup_ino,
-		__entry->page_cgroup_ino
+		__entry->page_cgroup_ino,
+		MAJOR(__entry->dev), MINOR(__entry->dev)
 	)
 );
 
 TRACE_EVENT(flush_foreign,
 
 	TP_PROTO(struct bdi_writeback *wb, unsigned int frn_bdi_id,
-		 unsigned int frn_memcg_id),
+		 unsigned int frn_memcg_id, dev_t dev),
 
-	TP_ARGS(wb, frn_bdi_id, frn_memcg_id),
+	TP_ARGS(wb, frn_bdi_id, frn_memcg_id, dev),
 
 	TP_STRUCT__entry(
 		__array(char,		name, 32)
 		__field(u64,		cgroup_ino)
 		__field(unsigned int,	frn_bdi_id)
 		__field(unsigned int,	frn_memcg_id)
+		__field(dev_t,		dev)
 	),
 
 	TP_fast_assign(
@@ -330,13 +334,15 @@ TRACE_EVENT(flush_foreign,
 		__entry->cgroup_ino	= __trace_wb_assign_cgroup(wb);
 		__entry->frn_bdi_id	= frn_bdi_id;
 		__entry->frn_memcg_id	= frn_memcg_id;
+		__entry->dev		= dev;
 	),
 
-	TP_printk("bdi %s: cgroup_ino=%llu frn_bdi_id=%u frn_memcg_id=%u",
+	TP_printk("bdi %s: cgroup_ino=%llu frn_bdi_id=%u frn_memcg_id=%u dev=%u:%u",
 		__entry->name,
 		__entry->cgroup_ino,
 		__entry->frn_bdi_id,
-		__entry->frn_memcg_id
+		__entry->frn_memcg_id,
+		MAJOR(__entry->dev), MINOR(__entry->dev)
 	)
 );
 #endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 55bd5d100caa..f634874bbcef 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3949,14 +3949,15 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
 	struct address_space *mapping = folio_mapping(folio);
 	struct inode *bdev_inode = mapping ? mapping->host : NULL;
 
-	trace_track_foreign_dirty(folio, wb);
-
 	if (memcg_bdev_frn_wq && bdev_inode &&
 	    sb_is_blkdev_sb(bdev_inode->i_sb)) {
+		trace_track_foreign_dirty(folio, wb, bdev_inode->i_rdev);
 		mem_cgroup_track_foreign_bdev(memcg, bdev_inode->i_rdev);
 		return;
 	}
 
+	trace_track_foreign_dirty(folio, wb, 0);
+
 	/*
 	 * Pick the slot to use.  If there is already a slot for @wb, keep
 	 * using it.  If not replace the oldest one which isn't being
@@ -4031,6 +4032,7 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
 		spin_lock_irqsave(&memcg->frn_lock, flags);
 		if (!ctx->inflight && ctx->dev) {
 			ctx->inflight = true;
+			trace_flush_foreign(wb, 0, 0, ctx->dev);
 			queue_work(memcg_bdev_frn_wq, &ctx->work);
 		}
 		spin_unlock_irqrestore(&memcg->frn_lock, flags);
@@ -4048,7 +4050,8 @@ void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
 		if (time_after64(frn->at, now - intv) &&
 		    atomic_read(&frn->done.cnt) == 1) {
 			frn->at = 0;
-			trace_flush_foreign(wb, frn->bdi_id, frn->memcg_id);
+			trace_flush_foreign(wb, frn->bdi_id, frn->memcg_id,
+					    0);
 			cgroup_writeback_by_id(frn->bdi_id, frn->memcg_id,
 					       WB_REASON_FOREIGN_FLUSH,
 					       &frn->done);
-- 
2.39.5