SSR allocate mode will be used when doing file defragment
if ATGC is working at the same time, that is because
set_page_private_gcing may make CURSEG_ALL_DATA_ATGC segment
type got in f2fs_allocate_data_block when defragment page
is writeback, which may cause file fragmentation is worse.

A file with 2 fragmentations is changed as following after defragment:

----------------file info-------------------
sensorsdata :
--------------------------------------------
dev       [254:48]
ino       [0x    3029 : 12329]
mode      [0x    81b0 : 33200]
nlink     [0x       1 : 1]
uid       [0x    27e6 : 10214]
gid       [0x    27e6 : 10214]
size      [0x  242000 : 2367488]
blksize   [0x    1000 : 4096]
blocks    [0x    1210 : 4624]
--------------------------------------------

file_pos   start_blk     end_blk        blks
       0    11361121    11361207          87
  356352    11361215    11361216           2
  364544    11361218    11361218           1
  368640    11361220    11361221           2
  376832    11361224    11361225           2
  385024    11361227    11361238          12
  434176    11361240    11361252          13
  487424    11361254    11361254           1
  491520    11361271    11361279           9
  528384     3681794     3681795           2
  536576     3681797     3681797           1
  540672     3681799     3681799           1
  544768     3681803     3681803           1
  548864     3681805     3681805           1
  552960     3681807     3681807           1
  557056     3681809     3681809           1
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>