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>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 97fbe93..bfb620e 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1136,7 +1136,8 @@
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]));
}