If gc_mode is set to GC_URGENT_LOW or GC_URGENT_MID, cost benefit GC
approach should be used, but if ATGC is enabled at the same time,
Age-threshold approach will be selected, which can only do amount of
GC and it is much less than the numbers of CB approach.
some traces:
f2fs_gc-254:48-396 [007] ..... 2311600.684028: f2fs_gc_begin: dev = (254,48), gc_type = Background GC, no_background_GC = 0, nr_free_secs = 0, nodes = 1053, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
f2fs_gc-254:48-396 [007] ..... 2311600.684527: f2fs_get_victim: dev = (254,48), type = No TYPE, policy = (Background GC, LFS-mode, Age-threshold), victim = 10, cost = 4294364975, ofs_unit = 1, pre_victim_secno = -1, prefree = 0, free = 44898
f2fs_gc-254:48-396 [007] ..... 2311600.714835: f2fs_gc_end: dev = (254,48), ret = 0, seg_freed = 0, sec_freed = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
f2fs_gc-254:48-396 [007] ..... 2311600.714843: f2fs_background_gc: dev = (254,48), wait_ms = 50, prefree = 0, free = 44898
f2fs_gc-254:48-396 [007] ..... 2311600.771785: f2fs_gc_begin: dev = (254,48), gc_type = Background GC, no_background_GC = 0, nr_free_secs = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:
f2fs_gc-254:48-396 [007] ..... 2311600.772275: f2fs_gc_end: dev = (254,48), ret = -61, seg_freed = 0, sec_freed = 0, nodes = 1562, dents = 2, imeta = 18, free_sec:44898, free_seg:44898, rsv_seg:239, prefree_seg:0
Fixes: 0e5e81114de1 ("f2fs: add GC_URGENT_LOW mode in gc_urgent")
Fixes: d98af5f45520 ("f2fs: introduce gc_urgent_mid mode")
Signed-off-by: Zhiguo Niu <zhiguo.niu@xxxxxxxxxx>