Confuse with WL_THRESHOLD

[Thang Dao Duy]

Hi everyone.
I used NANDsim and ubifs not for along time. Now, I have confused with
wear-leveling threshold. If i give parameter WL_THRESHOLD in Kernel is
small (example, the value is  3), then when i write a file size 2 MiB
to NAND about 200 times, it makes me cannot read EC and VID headers of
one PEB (example PEB 10). May be that PEB is bad ? And when i set the
WL_THRESHOLD is higher (the value is 20), i write a file 2MiB about
1000 times, nothing 's happen, i can read headers of any PEB. So can
you tell me what make this happen, and show me where in ubi source in
kernel.
Thanks.