3

Xubuntu Saucy with 4GB RAM. When the computer is restarted and immediately after login, about 500 MB of RAM is taken according to free -m. Then I run some programs and memory usage goes above 3 GM.

Now here is the problem: If I close all the open applications, still about 2.5 GB of memory is used but no thread accounts for all this memory. Here is the result of ps aux:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND  
root         1  0.0  0.0  27092  2680 ?        Ss   mar27   0:02 /sbin/init  
root         2  0.0  0.0      0     0 ?        S    mar27   0:00 [kthreadd]  
root         3  0.0  0.0      0     0 ?        S    mar27   0:25 [ksoftirqd/0]  
root         5  0.0  0.0      0     0 ?        S<   mar27   0:00 [kworker/0:0H]  
root         7  0.0  0.0      0     0 ?        S    mar27   0:15 [migration/0]  
root         8  0.0  0.0      0     0 ?        S    mar27   0:00 [rcu_bh]  
root         9  0.0  0.0      0     0 ?        S    mar27   0:00 [rcuob/0]  
root        10  0.0  0.0      0     0 ?        S    mar27   0:00 [rcuob/1]  
root        11  0.0  0.0      0     0 ?        S    mar27   0:24 [rcu_sched]  
root        12  0.0  0.0      0     0 ?        S    mar27   0:11 [rcuos/0]  
root        13  0.0  0.0      0     0 ?        S    mar27   0:12 [rcuos/1]  
root        14  0.0  0.0      0     0 ?        S    mar27   0:01 [watchdog/0]  
root        15  0.0  0.0      0     0 ?        S    mar27   0:01 [watchdog/1]  
root        16  0.0  0.0      0     0 ?        S    mar27   0:11 [migration/1]  
root        17  0.0  0.0      0     0 ?        S    mar27   0:22 [ksoftirqd/1]  
root        19  0.0  0.0      0     0 ?        S<   mar27   0:00 [kworker/1:0H]  
root        20  0.0  0.0      0     0 ?        S<   mar27   0:00 [khelper]  
root        21  0.0  0.0      0     0 ?        S    mar27   0:00 [kdevtmpfs]  
root        22  0.0  0.0      0     0 ?        S<   mar27   0:00 [netns]  
root        23  0.0  0.0      0     0 ?        S<   mar27   0:00 [writeback]  
root        24  0.0  0.0      0     0 ?        S<   mar27   0:00 [kintegrityd]  
root        25  0.0  0.0      0     0 ?        S<   mar27   0:00 [bioset]  
root        27  0.0  0.0      0     0 ?        S<   mar27   0:00 [kblockd]  
root        29  0.0  0.0      0     0 ?        S<   mar27   0:00 [ata_sff]  
root        30  0.0  0.0      0     0 ?        S    mar27   0:00 [khubd]  
root        31  0.0  0.0      0     0 ?        S<   mar27   0:00 [md]  
root        32  0.0  0.0      0     0 ?        S<   mar27   0:00 [devfreq_wq]  
root        35  0.0  0.0      0     0 ?        S    mar27   0:00 [khungtaskd]  
root        36  0.0  0.0      0     0 ?        S    mar27   0:05 [kswapd0]  
root        37  0.0  0.0      0     0 ?        SN   mar27   0:00 [ksmd]  
root        38  0.0  0.0      0     0 ?        SN   mar27   0:00 [khugepaged]  
root        39  0.0  0.0      0     0 ?        S    mar27   0:00 [fsnotify_mark]  
root        40  0.0  0.0      0     0 ?        S    mar27   0:00 [ecryptfs-kthrea]  
root        41  0.0  0.0      0     0 ?        S<   mar27   0:00 [crypto]  
root        53  0.0  0.0      0     0 ?        S<   mar27   0:00 [kthrotld]  
root        74  0.0  0.0      0     0 ?        S<   mar27   0:00 [deferwq]  
root        75  0.0  0.0      0     0 ?        S<   mar27   0:00 [charger_manager]  
root       122  0.0  0.0      0     0 ?        S<   mar27   0:00 [firewire]  
root       124  0.0  0.0      0     0 ?        S    mar27   0:00 [scsi_eh_0]  
root       125  0.0  0.0      0     0 ?        S    mar27   0:00 [scsi_eh_1]  
root       126  0.0  0.0      0     0 ?        S    mar27   0:00 [scsi_eh_2]  
root       127  0.0  0.0      0     0 ?        S    mar27   0:00 [scsi_eh_3]  
root       144  0.0  0.0      0     0 ?        S    mar27   0:03 [jbd2/sda6-8]  
root       145  0.0  0.0      0     0 ?        S<   mar27   0:00 [ext4-rsv-conver]  
root       146  0.0  0.0      0     0 ?        S<   mar27   0:00 [ext4-unrsv-conv]  
root       346  0.0  0.0      0     0 ?        S<   mar27   0:00 [cfg80211]  
root       347  0.0  0.0      0     0 ?        S<   mar27   0:00 [kpsmoused]  
root       392  0.0  0.0      0     0 ?        S<   mar27   0:00 [hd-audio0]  
102        531  0.0  0.0  31640  2500 ?        Ss   mar27   0:13 dbus-daemon --system --fork  
root       590  0.0  0.0  37140  1580 ?        Ss   mar27   0:00 /lib/systemd/systemd-logind  
root       591  0.0  0.0  83484  3324 ?        Ss   mar27   0:02 /usr/sbin/modem-manager  
root       592  0.0  0.0  19396  2116 ?        Ss   mar27   0:00 /usr/sbin/bluetoothd  
root       625  0.0  0.0      0     0 ?        S<   mar27   0:00 [krfcommd]  
root       636  0.0  0.1 271524  5588 ?        Ssl  mar27   0:21 NetworkManager  
root       659  0.0  0.1 284248  5392 ?        Sl   mar27   0:03 /usr/lib/policykit-1/polkitd --no-debug  
syslog     692  0.0  0.0 247476  1304 ?        Sl   mar27   0:19 rsyslogd -c5  
root       797  0.0  0.0  16056   548 ?        S    mar27   0:00 upstart-socket-bridge --daemon  
root       800  0.0  0.0  15668   516 ?        S    mar27   0:00 upstart-file-bridge --daemon  
root       851  0.0  0.0  24236   748 tty4     Ss+  mar27   0:00 /sbin/getty -8 38400 tty4  
root       854  0.0  0.0  24236   748 tty5     Ss+  mar27   0:00 /sbin/getty -8 38400 tty5  
root       860  0.0  0.0  24236   748 tty2     Ss+  mar27   0:00 /sbin/getty -8 38400 tty2  
root       863  0.0  0.0  24236   748 tty3     Ss+  mar27   0:00 /sbin/getty -8 38400 tty3  
root       872  0.0  0.0  24236   748 tty6     Ss+  mar27   0:00 /sbin/getty -8 38400 tty6  
root       932  0.0  0.0   4376   612 ?        Ss   mar27   0:00 acpid -c /etc/acpi/events -s /var/run/acpid.socket  
root       933  0.0  0.0  25804   900 ?        Ss   mar27   0:00 cron  
root       951  0.0  0.0 275628  3052 ?        SLsl mar27   0:00 lightdm  
root       994  1.4  2.7 300936 113208 tty7    Ss+  mar27 112:27 /usr/bin/X -core :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch  
root       997  0.0  0.0  24236   752 tty1     Ss+  mar27   0:00 /sbin/getty -8 38400 tty1  
root      1021  0.0  0.0 279004  4008 ?        Sl   mar27   0:06 /usr/lib/accountsservice/accounts-daemon  
root      1035  0.0  0.0      0     0 ?        S    mar27   0:00 [kauditd]  
root      1085  0.0  0.0 163808  2988 ?        Sl   mar27   0:00 lightdm --session-child 12 19  
root      1094  0.0  0.0  32692  2836 ?        Ss   mar27   0:11 /sbin/wpa_supplicant -B -P /run/sendsigs.omit.d/wpasupplicant.pid -u -s -O /var/run/wpa_supplicant  
rez       1144  0.0  0.0  37560  1848 ?        Ss   mar27   0:01 init --user  
rez       1195  0.0  0.0  12624    92 ?        Ss   mar27   0:00 ssh-agent  
rez       1200  0.0  0.0  32716  2572 ?        Ss   mar27   0:08 dbus-daemon --fork --session --address=unix:abstract=/tmp/dbus-S88cKKbWgL  
rez       1205  0.0  0.0  26516  1044 ?        Ss   mar27   0:00 upstart-event-bridge  
rez       1216  0.0  0.0   4440   576 ?        Ss   mar27   0:00 /bin/sh /etc/xdg/xfce4/xinitrc -- /etc/X11/xinit/xserverrc  
rez       1224  0.0  0.2 328460 11808 ?        Sl   mar27   0:11 xfce4-session  
rez       1229  0.0  0.0  34996   760 ?        S    mar27   0:00 upstart-file-bridge --daemon --user  
rez       1230  0.0  0.0  26520   528 ?        S    mar27   0:01 upstart-dbus-bridge --daemon --session --user --bus-name session  
rez       1232  0.0  0.0  26520   532 ?        S    mar27   0:01 upstart-dbus-bridge --daemon --system --user --bus-name system  
rez       1235  0.0  0.0  39360  2432 ?        S    mar27   0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd  
rez       1238  0.0  0.4 320204 16784 ?        Sl   mar27   3:51 xfwm4 --replace --display :0.0 --sm-client-id 273d07c4e-c10c-41ee-8cf9-2374cb32777e  
rez       1240  0.0  1.2 1151052 50204 ?       Sl   mar27   2:10 Thunar --sm-client-id 20caa2dc4-4174-44d3-82ef-fbb67bffe778 --daemon  
nobody    1242  0.0  0.0  39412  1340 ?        S    mar27   0:01 /usr/sbin/dnsmasq --no-resolv --keep-in-foreground --no-hosts --bind-interfaces --pid-file=/var/run/NetworkManager/dnsmasq.pid --listen-address=127.0.1.1 --conf-file=/var/run/NetworkManager/dnsmasq.conf --cache-size=0 --proxy-dnssec --enable-dbus=org.freedesktop.NetworkManager.dnsmasq --conf-dir=/etc/NetworkManager/dnsmasq.d  
rez       1266  0.0  0.7 526112 31824 ?        Sl   mar27   0:19 xfdesktop --display :0.0 --sm-client-id 2da06fe80-f4ae-4839-8b3b-91600fe2eb68  
rez       1267  0.0  0.6 348032 24372 ?        Ssl  mar27   0:20 xfsettingsd --display :0.0 --sm-client-id 2ba6a0c3b-f588-4771-9570-4b877c7f8c7f  
rez       1300  0.0  0.0 200876  2908 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfsd  
rez       1304  0.0  0.0 336860  2484 ?        Sl   mar27   0:00 /usr/lib/gvfs//gvfsd-fuse -f /run/user/1000/gvfs  
rez       1322  0.0  0.3 311836 12852 ?        Ssl  mar27   0:07 xfce4-power-manager --restart --sm-client-id 2ad69ea99-5f8a-4c94-afef-b10023557baf  
rez       1324  0.0  0.3 453000 15768 ?        Sl   mar27   0:01 /usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1  
rez       1334  0.0  0.0 337356  2724 ?        Sl   mar27   0:00 /usr/lib/at-spi2-core/at-spi-bus-launcher  
rez       1340  0.0  0.0  30488  1612 ?        S    mar27   0:00 /bin/dbus-daemon --config-file=/etc/at-spi2/accessibility.conf --nofork --print-address 3  
rez       1344  0.0  0.0 124920  2956 ?        Sl   mar27   0:01 /usr/lib/at-spi2-core/at-spi2-registryd --use-gnome-session  
rez       1347  0.0  0.7 958552 29336 ?        SLl  mar27   1:28 nm-applet  
rez       1352  0.0  0.9 344436 39920 ?        Ssl  mar27   0:25 xfce4-volumed  
rez       1355  0.0  0.0 368400  3804 ?        Sl   mar27   0:06 /usr/lib/x86_64-linux-gnu/indicator-application-service  
rez       1363  0.0  0.0  74664  2804 ?        S    mar27   0:21 xscreensaver -no-splash  
rez       1372  0.6  0.1 365508  5072 ?        Sl   mar27  49:29 /usr/bin/pulseaudio --start --log-target=syslog  
rtkit     1374  0.0  0.0 168920  1176 ?        SNl  mar27   0:02 /usr/lib/rtkit/rtkit-daemon  
root      1399  0.0  0.1 298576  4396 ?        Sl   mar27   0:07 /usr/lib/upower/upowerd  
rez       1497  0.0  0.1 450192  5196 ?        Sl   mar27   0:02 /usr/lib/gvfs/gvfs-udisks2-volume-monitor  
root      1500  0.0  0.1 436580  5668 ?        Sl   mar27   0:30 /usr/lib/udisks2/udisksd --no-debug  
rez       1536  0.0  0.0 200212  3276 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfs-mtp-volume-monitor  
rez       1624  0.0  0.0 289908  2892 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfs-afc-volume-monitor  
rez       1637  0.0  0.0 207980  2776 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfs-gphoto2-volume-monitor  
rez       1639  0.0  0.0  61360  2336 ?        S    mar27   0:00 /usr/lib/x86_64-linux-gnu/gconf/gconfd-2  
rez       1655  0.0  0.0  64324  2628 ?        S    mar27   0:01 /usr/bin/obex-data-server --no-daemon   
rez       1832  0.0  0.3 476124 15004 ?        Ssl  mar27   0:05 xfrun4  
rez       1943  0.0  0.7 450508 28392 ?        Sl   mar27   0:15 /usr/lib/gvfs/gvfsd-trash --spawner :1.9 /org/gtk/gvfs/exec_spaw/0  
root      1997  0.0  0.0  24444   596 ?        S    mar27   0:00 dbus-launch --autolaunch=42613f7aae1f969ac75e6e7252f27376 --binary-syntax --close-stderr  
root      1998  0.0  0.0  30652  1188 ?        Ss   mar27   0:00 //bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session  
rez       2942  0.0  0.0 302736  3708 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfsd-http --spawner :1.9 /org/gtk/gvfs/exec_spaw/1  
root      4058  0.0  0.0  39204  2312 ?        S    13:54   0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd  
root      4067  0.0  0.0 200752  2952 ?        Sl   13:54   0:00 /usr/lib/gvfs/gvfsd  
root      4071  0.0  0.0 271324  3000 ?        Sl   13:54   0:00 /usr/lib/gvfs//gvfsd-fuse -f /root/.gvfs  
root      4443  0.0  0.1 515556  5524 ?        Sl   13:54   0:00 /usr/lib/gvfs/gvfs-udisks2-volume-monitor  
root      4451  0.0  0.0 200344  3384 ?        Sl   13:54   0:00 /usr/lib/gvfs/gvfs-mtp-volume-monitor  
root      4455  0.0  0.0 289908  3296 ?        Sl   13:54   0:00 /usr/lib/gvfs/gvfs-afc-volume-monitor  
root      4460  0.0  0.0 207980  3344 ?        Sl   13:54   0:00 /usr/lib/gvfs/gvfs-gphoto2-volume-monitor  
root      5845  0.0  0.0  17320   632 ?        S    14:20   0:00 upstart-udev-bridge --daemon  
root      5848  0.0  0.0  42964  1952 ?        Ss   14:20   0:00 /lib/systemd/systemd-udevd --daemon  
root      7073  0.0  0.0 128452  2276 ?        Ss   mar27   0:01 smbd -F  
root      7076  0.0  0.0 129096  1124 ?        S    mar27   0:00 smbd -F  
root      7112  0.0  0.0  91400  1348 ?        Ss   mar27   0:16 nmbd -D  
root      9236  0.0  0.0  25248  1396 ?        Ss   mar30   0:03 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
root     10401  0.0  0.0  25248  1368 ?        Ss   mar30   0:04 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
rez      12137  0.0  0.1 125468  4216 ?        Sl   mar27   0:02 /usr/lib/gvfs/gvfsd-metadata  
root     12267  0.0  0.0      0     0 ?        S    14:42   0:00 [kworker/1:3]  
rez      12435  0.0  0.0 178216  2648 ?        Sl   mar27   0:00 /usr/lib/dconf/dconf-service  
root     13050  0.0  0.0      0     0 ?        S<   14:44   0:00 [hci0]  
root     13051  0.0  0.0      0     0 ?        S<   14:44   0:00 [hci0]  
dnsmasq  13805  0.0  0.0  39416  1028 ?        S    15:24   0:00 /usr/sbin/dnsmasq -x /var/run/dnsmasq/dnsmasq.pid -u dnsmasq -r /var/run/dnsmasq/resolv.conf -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new  
root     13873  0.0  0.0      0     0 ?        S    15:24   0:07 [irq/18-b43]  
root     13875  0.0  0.0  25248  1344 ?        Ss   15:24   0:01 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
root     13884  0.0  0.0  20944   988 ?        S    15:24   0:02 /bin/bash /usr/bin/ap-hotspot start  
rez      14672  0.0  0.1 684664  6128 ?        Sl   mar27   0:01 /usr/lib/indicator-sound-gtk2/indicator-sound-service  
root     15097  0.0  0.0 195828  3936 ?        Sl   mar27   0:03 /usr/lib/udisks/udisks-daemon  
root     15098  0.0  0.0  47844   528 ?        S    mar27   0:00 udisks-daemon: not polling any devices  
rez      15264  0.0  0.0 374624  3600 ?        SLl  mar27   0:00 /usr/bin/gnome-keyring-daemon --start --foreground --components=secrets  
root     15913  0.0  0.0      0     0 ?        S    16:17   0:04 [kworker/0:2]  
root     16432  0.0  0.0      0     0 ?        S<   mar27   0:00 [kworker/1:1H]  
root     16733  0.0  0.0      0     0 ?        S    16:37   0:00 [kworker/u4:0]  
rez      16991  0.0  0.7 544484 30484 ?        Sl   mar30   0:00 /usr/bin/python /usr/bin/blueman-applet  
root     17133  0.0  0.0  10244  3736 ?        S    16:46   0:00 /sbin/dhclient -d -sf /usr/lib/NetworkManager/nm-dhcp-client.action -pf /run/sendsigs.omit.d/network-manager.dhclient-eth0.pid -lf /var/lib/NetworkManager/dhclient-1d839b90-39a2-4362-9cb0-0cba8724ef39-eth0.lease -cf /var/lib/NetworkManager/dhclient-eth0.conf eth0  
root     17918  0.0  0.0  72940  2636 ?        Ss   mar27   0:00 /usr/sbin/cups-browsed  
rez      18213  0.0  0.5 462292 22604 ?        Sl   mar27   0:01 artha  
root     18672  0.0  0.0  25248  1356 ?        Ss   mar27   0:03 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
rez      18679  0.0  0.0  24444   596 ?        S    mar27   0:00 dbus-launch --autolaunch=42613f7aae1f969ac75e6e7252f27376 --binary-syntax --close-stderr  
rez      18680  0.0  0.0  30524  1128 ?        Ss   mar27   0:00 //bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session  
rez      18685  0.0  0.0  39232  2208 ?        S    mar27   0:00 /usr/lib/x86_64-linux-gnu/xfce4/xfconf/xfconfd  
rez      18688  0.0  0.0 200752  2856 ?        Sl   mar27   0:00 /usr/lib/gvfs/gvfsd  
root     19329  0.0  0.0      0     0 ?        S    17:35   0:00 [kworker/0:1]  
root     19677  0.0  0.0      0     0 ?        S    mar30   0:00 [jbd2/sda1-8]  
root     19678  0.0  0.0      0     0 ?        S<   mar30   0:00 [ext4-rsv-conver]  
root     19679  0.0  0.0      0     0 ?        S<   mar30   0:00 [ext4-unrsv-conv]  
root     19967  0.0  0.0      0     0 ?        S    17:52   0:00 [kworker/u4:1]  
root     19996  0.0  0.0  61356  2576 ?        S    mar30   0:00 /usr/lib/x86_64-linux-gnu/gconf/gconfd-2  
root     20457  0.0  0.0      0     0 ?        S    18:03   0:00 [kworker/u4:2]  
root     20532  0.0  0.0  25248  1396 ?        Ss   mar31   0:03 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
rez      20659  1.3  0.3 456460 15952 ?        Sl   18:07   0:00 xfce4-terminal  
rez      20663  0.0  0.0  14832   816 ?        S    18:07   0:00 gnome-pty-helper  
rez      20664  0.1  0.0  30540  3372 pts/5    Ss   18:07   0:00 bash  
root     20727  0.0  0.0  15612   624 ?        S    18:07   0:00 sleep 5  
root     20728  0.6  0.0  69172  2292 pts/5    S+   18:07   0:00 sudo ps aux  
root     20729  0.0  0.0  26856  1348 pts/5    R+   18:08   0:00 ps aux  
root     22673  0.0  0.0  74436  2912 ?        Ss   mar28   0:00 /usr/sbin/cupsd -F  
root     22880  0.0  0.0  25248  1372 ?        Ss   mar28   0:03 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  
root     26957  0.0  0.0      0     0 ?        S<   mar31   0:00 [kworker/u5:2]  
rez      28053  0.0  0.5 440980 22640 ?        Sl   mar30   1:41 xfce4-panel  
rez      28057  0.0  0.2 168856 10340 ?        S    mar30   0:00 /usr/lib/x86_64-linux-gnu/xfce4/panel/wrapper /usr/lib/x86_64-linux-gnu/xfce4/panel/plugins/libactions.so 9 14680107 actions Action Buttons Log out, lock or other system actions   
rez      28059  0.0  0.1 158580  7540 ?        S    mar30   0:00 /usr/lib/x86_64-linux-gnu/xfce4/panel/wrapper /usr/lib/x86_64-linux-gnu/xfce4/panel/plugins/libsystray.so 4 14680108 systray Notification Area Area where notification icons appear   
rez      28060  0.0  0.5 517992 23188 ?        Sl   mar30   0:07 /usr/lib/x86_64-linux-gnu/xfce4/panel-plugins/xfce4-indicator-plugin  5 14680109 indicator Indicator Plugin An indicator of something that needs your attention on the desktop   
rez      28062  0.0  0.4 452116 17196 ?        Sl   mar30   0:06 /usr/lib/x86_64-linux-gnu/xfce4/panel/wrapper /usr/lib/x86_64-linux-gnu/xfce4/panel-plugins/libnotes.so 12 14680121 xfce4-notes-plugin Notes Ideal for your quick notes   
rez      28063  0.0  0.5 260536 21088 ?        Sl   mar30   0:15 /usr/lib/x86_64-linux-gnu/xfce4/panel-plugins/xfce4-xkb-plugin  28 14680122 xkb-plugin Keyboard Layouts Keyboard layouts setup and switch plugin   
root     28891  0.0  0.0      0     0 ?        S    mar31   0:20 [kworker/1:1]  
root     29208  0.0  0.0      0     0 ?        S<   09:43   0:00 [kworker/u5:1]  
avahi    29548  0.0  0.0  32348  1584 ?        S    mar28   0:00 avahi-daemon: registering [rez-Vostro.local]  
avahi    29550  0.0  0.0  32228   420 ?        S    mar28   0:00 avahi-daemon: chroot helper  
root     30645  0.0  0.0  25248  1356 ?        Ss   mar29   0:03 hostapd -B /etc/hostapd-hotspot.conf -f /tmp/hostapd.log  

and here the output of free -m

           total       used       free     shared    buffers     cached
Mem:          3949       2512       1436          0        241       1164
-/+ buffers/cache:       1106       2842
Swap:         1715         55       1660

As you can see (even though not all threads are shown in the picture) the memory taken by the threads won't add up to anything close to 2512/3949=64%.

So, what is taking up all this memory? Can it be the kernel treads (whose amount of memory is not displayed) or a leak in Ubuntu itself?

Something which may be relevant is that the ammount of used memory shown by XFCE task manager is significantly lower than what free -m shows.

4
  • What was running at the moment you did the free -m ? Can you provide a ps aux output too ?
    – Benoit
    Apr 1, 2014 at 13:25
  • As I said I closed all the applications I had opened before doing free -m. Now I closed them again and did ps aux.
    – Reza
    Apr 1, 2014 at 16:17
  • 4
    Your system is actually using only 1.1 GB of RAM. Linux caches some files to RAM for quick access, so it appears that 2.5 GB is being used. The -/+ buffers/cache line shows the RAM usage excluding buffers and cache files. Apr 1, 2014 at 18:24

1 Answer 1

2

By default, freeshows also memory used by cache and buffers

In the free -m output, as already said in the comments, you have to look to the line

-/+ buffers/cache:       1106       2842

to see exactly the quantity of memory used by applications, kernel and modules. In this case, you are using 1106 MB, which is almost 28% of the total memory. The rest is taken by the usual buffers and cache that helps the kernel to access files quicker.

The ps output shows the memory used by process

In the ps output I see that you still have the whole graphical desktop running, with a lot of components running. They take about 13% of the memory.

And the modules...

The delta between the ps calculation and the free is constituted of the memory taken by the kernel and the modules loaded. As the size column of the lsmod output only displays the size of the module on the filesystem (so the syse of the .ko file from which this module is loaded) it is not reliable to measure the memory used by them. A more reliable approach to measure the memory used by modules is to use the slabtop utilities (installed from the procps package.

Also see the content of /proc/meminfo, it gives the total usage of the Slab memory, the memory used to efficiently allocate memory to kernel objects. (See Wikipedia for more details on Slab).

In conclusion

Memory usage is a complex domain, and you will need more than one tool to see in details which piece of memory is used by what. free, ps, slabtop, /proc/meminfo content, top, vmstat, htop, ... all they can bring a piece of information helpfull to build the full picture on your particular memory usage.

1
  • +1 for "memory usage is a complex domain" - because memory management is a complex domain. Jul 22, 2014 at 21:58

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