ETFS CPU utilization

We are using ETFS for a NAND flash device. What we have
observed is periodically the NAND flash driver using ETFS
uses almost 100% CPU (seend from hogs).

Following is the normal thread state of NAND flash driver:
pid tid name prio STATE Blocked
9 1 /boot/fs-etfs-nand 10r RECEIVE 1
9 2 /boot/fs-etfs-nand 10r NANOSLEEP

When the CPU utilization shoots to 100%, following is the
thread state for the NAND flash driver:

9 1 /boot/fs-etfs-nand 10r MUTEX 9-02 #1
9 2 /boot/fs-etfs-nand 10r READY

It is also observed that at this time, the size of file
being appended on the NAND flash device is not increasing -
we have created a test program that is appending data to
the file continuously.

I suspect that this is happening due to some houskeeping in
ETFS (background defragmentation?).

This severely impacts system as this halts all other
processes for almost 10 seconds while NAND driver is
hogging the CPU.

Any inputs would be appreciated.