btrfs: fix dirtied pages accounting on sub-page writes

When doing 1KB sequential writes to the same page,
balance_dirty_pages_ratelimited_nr() should be called once instead of 4
times, the latter makes the dirtier tasks be throttled much too heavy.

Fix it with proper de-accounting on clear_page_dirty_for_io().

CC: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 97fbe939c050..bfb620ead295 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1136,7 +1136,8 @@ again:
                                      GFP_NOFS);
         }
         for (i = 0; i < num_pages; i++) {
-                clear_page_dirty_for_io(pages[i]);
+                if (clear_page_dirty_for_io(pages[i]))
+                        account_page_redirty(pages[i]);
                 set_page_extent_mapped(pages[i]);
                 WARN_ON(!PageLocked(pages[i]));
         }