writeback: Add tracepoint to track pending inode switches

Add trace_inode_switch_wbs_queue tracepoint to allow insight into how
many inodes are queued to switch their bdi_writeback structure.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index af5f396449f16e3c72b4a15b15e8431357f51785..52129267e3bd8a61f7806ff1d1961fa90d174edd 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -667,6 +667,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
 
        isw->inodes[0] = inode;
 
+       trace_inode_switch_wbs_queue(inode->i_wb, new_wb, 1);
        wb_queue_isw(new_wb, isw);
        return;
 
@@ -752,6 +753,7 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb)
                return restart;
        }
 
+       trace_inode_switch_wbs_queue(wb, new_wb, nr);
        wb_queue_isw(new_wb, isw);
 
        return restart;

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 1e23919c0da981319f3deee29b482116c73a8064..c08aff044e807386381e6e0e2d52075d014d8001 100644 (file)
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -213,6 +213,35 @@ TRACE_EVENT(inode_foreign_history,
        )
 );
 
+TRACE_EVENT(inode_switch_wbs_queue,
+
+       TP_PROTO(struct bdi_writeback *old_wb, struct bdi_writeback *new_wb,
+                unsigned int count),
+
+       TP_ARGS(old_wb, new_wb, count),
+
+       TP_STRUCT__entry(
+               __array(char,           name, 32)
+               __field(ino_t,          old_cgroup_ino)
+               __field(ino_t,          new_cgroup_ino)
+               __field(unsigned int,   count)
+       ),
+
+       TP_fast_assign(
+               strscpy_pad(__entry->name, bdi_dev_name(old_wb->bdi), 32);
+               __entry->old_cgroup_ino = __trace_wb_assign_cgroup(old_wb);
+               __entry->new_cgroup_ino = __trace_wb_assign_cgroup(new_wb);
+               __entry->count          = count;
+       ),
+
+       TP_printk("bdi %s: old_cgroup_ino=%lu new_cgroup_ino=%lu count=%u",
+               __entry->name,
+               (unsigned long)__entry->old_cgroup_ino,
+               (unsigned long)__entry->new_cgroup_ino,
+               __entry->count
+       )
+);
+
 TRACE_EVENT(inode_switch_wbs,
 
        TP_PROTO(struct inode *inode, struct bdi_writeback *old_wb,