writeback: trace event writeback_queue_io

Note that it adds a little overheads to account the moved/enqueued
inodes from b_dirty to b_io. The "moved" accounting may be later used to
limit the number of inodes that can be moved in one shot, in order to
keep spinlock hold time under control.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5185fad48b62..6caa98247a5b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -248,15 +248,16 @@ static bool inode_dirtied_after(struct inode *inode, unsigned long t)
 /*
  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
  */
-static void move_expired_inodes(struct list_head *delaying_queue,
+static int move_expired_inodes(struct list_head *delaying_queue,
                                struct list_head *dispatch_queue,
-                                unsigned long *older_than_this)
+                               unsigned long *older_than_this)
 {
         LIST_HEAD(tmp);
         struct list_head *pos, *node;
         struct super_block *sb = NULL;
         struct inode *inode;
         int do_sb_sort = 0;
+        int moved = 0;
 
         while (!list_empty(delaying_queue)) {
                 inode = wb_inode(delaying_queue->prev);
@@ -267,12 +268,13 @@ static void move_expired_inodes(struct list_head *delaying_queue,
                         do_sb_sort = 1;
                 sb = inode->i_sb;
                 list_move(&inode->i_wb_list, &tmp);
+                moved++;
         }
 
         /* just one sb in list, splice to dispatch_queue and we're done */
         if (!do_sb_sort) {
                 list_splice(&tmp, dispatch_queue);
-                return;
+                goto out;
         }
 
         /* Move inodes from one superblock together */
@@ -284,6 +286,8 @@ static void move_expired_inodes(struct list_head *delaying_queue,
                                 list_move(&inode->i_wb_list, dispatch_queue);
                 }
         }
+out:
+        return moved;
 }
 
 /*
@@ -299,9 +303,11 @@ static void move_expired_inodes(struct list_head *delaying_queue,
  */
 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
 {
+        int moved;
         assert_spin_locked(&wb->list_lock);
         list_splice_init(&wb->b_more_io, &wb->b_io);
-        move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
+        moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
+        trace_writeback_queue_io(wb, older_than_this, moved);
 }
 
 static int write_inode(struct inode *inode, struct writeback_control *wbc)