Computer freezing on almost full RAM, possibly disk cache problem
To fix this problem I have found that you need to set the following setting to something around 5%-6% of your total physical RAM, divided by the number of cores in the computer:
sysctl -w vm.min_free_kbytes=65536
Keep in mind that this is a per-core setting, so if I have 2GB RAM and two Cores, then I calculated 6% of only 1 GB and added a little extra just to be safe.
This forces the computer to try to keep this amount of RAM free, and in doing so limits the ability to cache disk files. Of course it still tries to cache them and immediately swap them out, so you should probably limit your swapping as well:
sysctl -w vm.swappiness=5
(100 = swap as often as possible, 0= swap only on total necessity)
The result is that linux no longer randomly decides to load a whole movie file of approx 1GB in ram while watching it, and killing the machine in doing so.
Now there is enough reserved space to avoid memory starvation, which aparrently was the problem (seeing as there are no more freezes like before).
After testing for a day - lockups are gone, sometimes there are minor slowdowns, because stuff gets cached more often, but I can live with that if I dont have to restart computer every few hours.
The lesson here is - default memory management is just one of use cases and is not allways the best, even though some people try to suggest otherwise - home entertainment ubuntu should be configured differently than server.
You probably want to make these settings permanent by adding them to your /etc/sysctl.conf like this:
vm.swappiness=5
vm.min_free_kbytes=65536
This happened for me in a new install of Ubuntu 14.04.
In my case, it had nothing to do with sysctl issues mentioned.
Instead, the problem was that the swap partition's UUID was different during installation than it was after installation. So my swap was never enabled, and my machine would lock up after a few hours use.
The solution was to check the current UUID of the swap partition with
sudo blkid
and then sudo nano /etc/fstab to replace the incorrect swap's UUID value with the one reported by blkid.
A simple reboot to affect the changes, and voila.
Nothing worked for me!!
So I wrote a script to monitor memory usage. It will first try to clear RAM cache if the memory consumption increases a threshold. You can configure this threshold on the script. If memory consumption doesn't come below the threshold even then, it will start killing processes on by one in decreasing order of memory consumption until the memory consumption is below the threshold. I have set it to 96% by default. You can configure it by changing the value of variable RAM_USAGE_THRESHOLD in the script.
I agree that killing processes which consume high memory is not the perfect solution, but it's better to kill ONE application instead of losing ALL the work!! the script will send you desktop notification if RAM usage increases the threshold. It will also notify you if it kills any process.
#!/usr/bin/env python
import psutil, time
import tkinter as tk
from subprocess import Popen, PIPE
import tkinter
from tkinter import messagebox
root = tkinter.Tk()
root.withdraw()
RAM_USAGE_THRESHOLD = 96
MAX_NUM_PROCESS_KILL = 100
def main():
if psutil.virtual_memory().percent >= RAM_USAGE_THRESHOLD:
# Clear RAM cache
mem_warn = "Memory usage critical: {}%\nClearing RAM Cache".\
format(psutil.virtual_memory().percent)
print(mem_warn)
Popen("notify-send \"{}\"".format(mem_warn), shell=True)
print("Clearing RAM Cache")
print(Popen('echo 1 > /proc/sys/vm/drop_caches',
stdout=PIPE, stderr=PIPE,
shell=True).communicate())
post_cache_mssg = "Memory usage after clearing RAM cache: {}%".format(
psutil.virtual_memory().percent)
Popen("notify-send \"{}\"".format(post_cache_mssg), shell=True)
print(post_cache_mssg)
if psutil.virtual_memory().percent < RAM_USAGE_THRESHOLD:
print("Clearing RAM cache saved the day")
return
# Kill top C{MAX_NUM_PROCESS_KILL} highest memory consuming processes.
ps_killed_notify = ""
for i, ps in enumerate(sorted(psutil.process_iter(),
key=lambda x: x.memory_percent(),
reverse=True)):
# Do not kill root
if ps.pid == 1:
continue
elif (i > MAX_NUM_PROCESS_KILL) or \
(psutil.virtual_memory().percent < RAM_USAGE_THRESHOLD):
messagebox.showwarning('Killed proccess - save_hang',
ps_killed_notify)
Popen("notify-send \"{}\"".format(ps_killed_notify), shell=True)
return
else:
try:
ps_killed_mssg = "Killed {} {} ({}) which was consuming {" \
"} % memory (memory usage={})". \
format(i, ps.name(), ps.pid, ps.memory_percent(),
psutil.virtual_memory().percent)
ps.kill()
time.sleep(1)
ps_killed_mssg += "Current memory usage={}".\
format(psutil.virtual_memory().percent)
print(ps_killed_mssg)
ps_killed_notify += ps_killed_mssg + "\n"
except Exception as err:
print("Error while killing {}: {}".format(ps.pid, err))
else:
print("Memory usage = " + str(psutil.virtual_memory().percent))
root.update()
if __name__ == "__main__":
while True:
try:
main()
except Exception as err:
print(err)
time.sleep(1)
Save the code in a file say save_hang.py. Run the script as:
sudo python save_hang.py
Please note that this script is compatible for Python 3 only and requires you to install tkinter package. you can install it as:
sudo apt-get install python3-tk
Hope this helps...