This is a rework of journal credits fix patch in the ext4 patch queue.
The patch series contains

- patch 1: helper funtions for journal credits calculation and fix the
writepage/write_begin on nonextent files
- patch 2: journal credit fix wirtepahe/write_begin for extents files,
and migration
- patch 3: credit fix for dio, fallocate
-patch 4: rebase ext4_da_writepages_rework patch
- patch 5: credit fix for delalloc writepages
-patch 6: credit fix for defrag


Mingming