writeback: Add a 'reason' to wb_writeback_work

This creates a new 'reason' field in a wb_writeback_work
structure, which unambiguously identifies who initiates
writeback activity.  A 'wb_reason' enumeration has been
added to writeback.h, to enumerate the possible reasons.

The 'writeback_work_class' and tracepoint event class and
'writeback_queue_io' tracepoints are updated to include the
symbolic 'reason' in all trace events.

And the 'writeback_inodes_sbXXX' family of routines has had
a wb_stats parameter added to them, so callers can specify
why writeback is being started.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 986e2388f031..7fa73a3b2120 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2241,7 +2241,7 @@ static int ext4_nonda_switch(struct super_block *sb)
          * start pushing delalloc when 1/2 of free blocks are dirty.
          */
         if (free_blocks < 2 * dirty_blocks)
-                writeback_inodes_sb_if_idle(sb);
+                writeback_inodes_sb_if_idle(sb, WB_REASON_FS_FREE_SPACE);
 
         return 0;
 }