JFFS2: real free capacity of the partition

[Sergei Poselenov <sposelenov@emcraft.com>]

Hello,

Probably this is a trivial question and won't take much of your time.

A simple test on a JFFS2 partition:

# df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/mtdblock1            1024       376       648  37% /etc
# dd if=/dev/urandom of=tmp bs=1024 count=2900
dd: tmp: No space left on device
# rm tmp
# df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/mtdblock1            1024       372       652  36% /etc

Why additional space appeared?

I've noted, that this effect:
- appeared only on the well-used partition, not on the
   fresh-created one.
- appeared only after filling up the device
- appeared only once. On subsequent tests, the free space was
reported without magic increases.


Is this is an effect of the JFFS2 garbage collector?
Is there any method to learn the real available capacity of the
mounted partition?

Thanks in advance,
Sergei