Ubuntu – Ubuntu 12.04 questionable RAM usage, mouse lags, windows fade slowly and programs hang…after a few hours things return to normal

I've solved a similar problem with a memory/cpu watcher script and just have it kill any processes that it sees that have more than x ram or y memory for longer than t seconds. That doesn't solve the problem of reserving CPU/Mem for the OS, but it is a workaround until you find a better answer (And when you do, share it with me, because I got here looking for the same thing)

#!/bin/bash

# Kill POS if we're doing stupid shit.
HOG_COUNTER=0
while true; do
    # This is pulling CPU, change the awk column from 9 to something
    # that you want to check against.
    HOG=$(top -b -n 1 | grep pos2 | awk '$9 > 90 {print $1}')
    # If the hog variable is not empty, add some counter info - we don't
    # want to catch periodic spikes, we want to catch consistent offenders.
    if [ ! -z "$HOG" ]; then
        counter_time=$(date)
        HOG_COUNTER=$(expr ${HOG_COUNTER} + 1)
        echo "$counter_time - Found a hog: $HOG - ${HOG_COUNTER} counters." >> high_mem_kill_log
    else
        HOG_COUNTER=0
    fi
    # If we have more than 2 counters (3 or more) then we kill the process
    # that's doing it.
    if [ $HOG_COUNTER -gt 2 ]; then
        kill_time=$(date)
        echo "$kill_time - Found a hog: $HOG.  $HOG_COUNTER counters.  Killing $HOG." >> high_mem_kill_log
        kill $HOG
    fi
    sleep 30s
done

Based on personal experience, a swap file might be better utilized than a swap partition in newer versions of Ubuntu. You could try creating a swap file and disabling the swap partition and see how it works for you. To do so, please follow these steps:

1. Create the swap file ( 8 Gib ):

   sudo fallocate -l 8G /swapfile

2. Give the file right permissions to limit unneeded access:

   sudo chmod 600 /swapfile

3. Prepare the file as a swap area:

   sudo mkswap /swapfile

4. Activate the swap file:

   sudo swapon /swapfile

5. Deactivate the swap partition:

   sudo swapoff /dev/sda2

Test how your system swap behaves now.

Notice: ( except for the creation of the /swapfile ), these changes made to swap volumes are temporary and will be cleared after reboot. If you wish to make changes permanent,

• please edit your /etc/fstab file

  sudo nano /etc/fstab

• Add this line to the end of the file /swapfile swap swap defaults 0 0

  example:

  /dev/sda2 none swap sw 0 0 /swapfile swap swap defaults 0 0

• Comment out the line with the swap partition ( /dev/sda2 ) by adding # before it

  example:

  # /dev/sda2 none swap sw 0 0 /swapfile swap swap defaults 0 0

• Save the changes by pressing Ctrl + X then Y then Enter

fallocate or dd:

Thank you to @heynnema for raising this concern in the comments section below:

no, don't use fallocate to create /swapfile, use dd. Search for info about this here on AU.

I assume the concern is regarding the possibility of fallocate creating file holes which basically are portions of a file that contain null characters and are not stored in any data block on the disk. This in turn, if present, would render the swap file unusable.

To address this concern, let us have a look at the odds of fallocate creating file holes and the consequences of that.

It turns out:

• fallocate will not normally create holes unless it is operated on a preexisting file and the option --punch-hole is specified. Please read Ubuntu Manpage - fallocate

• fallocate --length 8GiB swapfile is suggested to create a swap file on Ubuntu man pages, please read Ubuntu Manpage - mkswap

• After all, if the created file contained holes in it, sudo swapon will throw an error skipping - it appears to have holes. and in this rare case which I haven't faced or heard of yet, the solution is simple. Just use dd to create the file in step # 1 above and move on. Do it as follows:

  sudo dd if=/dev/zero of=/swapfile bs=1024 count=8388608

  or as @v_mil did it:

  sudo dd if=/dev/zero of=/swapfile bs=1048576 count=8192

In short, this concern is not worrying enough to give up on the speed gained by using fallocate.