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Hello. Sorry for delay.

Memory usage didn't derectly depends on bandwidth - it
depends on number of active connections:

# ps -o cmd 7341
fprobe -ieth0 -p -fip -B4096 -r2 -v7 -q10000 localhost:2055

# kill -s USR1 7341;tail /var/log/syslog
fprobe[7341]: [DEBUG]: I: received:43508145/17325
(16845974727) pending:0/36
fprobe[7341]: [DEBUG]: I: ignored:0 lost:0+0 dropped:0
fprobe[7341]: [DEBUG]: I: cache:1252/2 emit:7352819/260335/0
fprobe[7341]: [DEBUG]: I: memory:20000/8746 (1280032)

There is allocated two memory bulks, 10000 flows within
each. 10000 flows occupied by pending queue, 1254 - by
active connections and 8746 - free. Each flow takes about 64
bytes. 20000 * 64 ~ 1280032. This is normal.

So, recompile your fprobe with --enable-debug=I and see what
happening.