raspbian - What uses the memory on raspberry pi? -

on pi after start there no free memory, can not found, waht uses it:

pi@node1 ~ $ cat /proc/cpuinfo processor       : 0 model name      : armv6-compatible processor rev 7 (v6l) bogomips        : 2.00 features        : half thumb fastmult vfp edsp java tls cpu implementer : 0x41 cpu architecture: 7 cpu variant     : 0x0 cpu part        : 0xb76 cpu revision    : 7  hardware        : bcm2708 revision        : 0013 serial          : 00000000bf2e5e5c  pi@node1 ~ $ uname -a linux node1 4.0.7+ #801 preempt tue jun 30 18:15:24 bst 2015 armv6l gnu/linux  pi@node1 ~ $ head -n1 /etc/issue raspbian gnu/linux 7 \n \l  pi@node1 ~ $ grep memtotal /proc/meminfo memtotal:         493868 kb  pi@node1 ~ $ grep "model name" /proc/cpuinfo model name      : armv6-compatible processor rev 7 (v6l)  pi@node1 ~ $ ps -eo pmem,pcpu,vsize,pid,cmd | sort -k 1 -nr | head -5  0.6  0.2   6244  2377 -bash  0.3  0.0   6748  2458 sort -k 1 -nr  0.3  0.0   4140  2457 ps -eo pmem,pcpu,vsize,pid,cmd  0.2  0.1   9484  2376 sshd: pi@pts/0  0.2  0.1   5600  2236 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 104:107  pi@node1 ~ $ free              total       used       free     shared    buffers     cached mem:        493868     478364      15504          0        500       4956 -/+ buffers/cache:     472908      20960 swap:       102396        116     102280 

i not linux expert, if understand right, there 15mb free memory, no task uses more 0.6%. why not there more free?

memory not exclusively allocated processes.

• the bootloader , init ram filesystem stored in memory.
• the kernel (could big) loaded memory.
• the kernel reserve memory it's processes. ps shows 0.0% these system processes.
• driver allocate buffer memory
• the graphics card needs memory
• if have not configured swap space on harddrive or sd card, uses memory.
• the network system allocates memory unix sockets , shared memory.
• 100 processes 0.1 % 10%.

and, if start process , stop not of memory released. try it. show memory usage free. start process need memory. stop process , use free again. bet there more memory usage before.

edit

here example of pi less memory usage. have no problems running java on it. have wlan dongle , original noir cam installed.

i installed raspbian wheezy. used kernel compiled sources:

> uname -a linux raspberrypi 3.18.14+ #2 preempt sun may 31 20:19:04 utc 2015 armv6l gnu/linux  > head -n1 /etc/issue raspbian gnu/linux 7 \n \l 

on pi can run java -version in acceptable period of time.

time java -version java version "1.8.0" java(tm) se runtime environment (build 1.8.0-b132) java hotspot(tm) client vm (build 25.0-b70, mixed mode)  real    0m1.012s user    0m0.800s sys     0m0.190s 

here memory footprint

> free              total      used       free       shared   buffers   cached mem:        380816     138304     242512     0        8916      96728 -/+ buffers/cache:      32660     348156   swap:       102396          0     102396