ext4: fix fio regression

We (Linux Kernel Performance project) found a regression introduced
by commit:

  f7fec032aa ext4: track all extent status in extent status tree

The commit causes about 20% performance decrease in fio random write
test. Profiler shows that rb_next() uses a lot of CPU time. The call
stack is:

  rb_next
  ext4_es_find_delayed_extent
  ext4_map_blocks
  _ext4_get_block
  ext4_get_block_write
  __blockdev_direct_IO
  ext4_direct_IO
  generic_file_direct_write
  __generic_file_aio_write
  ext4_file_write
  aio_rw_vect_retry
  aio_run_iocb
  do_io_submit
  sys_io_submit
  system_call_fastpath
  io_submit
  td_io_getevents
  io_u_queued_complete
  thread_main
  main
  __libc_start_main

The cause is that ext4_es_find_delayed_extent() doesn't have an
upper bound, it keeps searching until a delayed extent is found.
When there are a lots of non-delayed entries in the extent state
tree, ext4_es_find_delayed_extent() may uses a lot of CPU time.

Reported-by: LKP project <lkp@linux.intel.com>
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index d0e686402df8..8ee15b97cd38 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -2139,7 +2139,7 @@ TRACE_EVENT(ext4_es_remove_extent,
                   __entry->lblk, __entry->len)
 );
 
-TRACE_EVENT(ext4_es_find_delayed_extent_enter,
+TRACE_EVENT(ext4_es_find_delayed_extent_range_enter,
         TP_PROTO(struct inode *inode, ext4_lblk_t lblk),
 
         TP_ARGS(inode, lblk),
@@ -2161,7 +2161,7 @@ TRACE_EVENT(ext4_es_find_delayed_extent_enter,
                   (unsigned long) __entry->ino, __entry->lblk)
 );
 
-TRACE_EVENT(ext4_es_find_delayed_extent_exit,
+TRACE_EVENT(ext4_es_find_delayed_extent_range_exit,
         TP_PROTO(struct inode *inode, struct extent_status *es),
 
         TP_ARGS(inode, es),