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After the system starts, in a few minutes my memory cache fills up and it starts using the swap. Here's a screenshot of /proc/meminfo.

memory

However, if I can disable this process / clean the cache once after that, I think my system will speed up to some extent. Correct me if I am wrong here.

I have also tried Bleachbit memory cleaning, but it doesn't seem to clean the memory cache properly. Also, the feature is still in an experimental stage.

bleachbit memory

There was already a similar question posted here: How can I disable the prefetch cache?, but it was regarding Ubuntu Server, and also the answers involved manual settings etc.

So, I want to know if there's some software for disabling/enabling Memory Cache for Ubuntu 12.04.

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Bharadwaj Srigiriraju
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4 Answers4

76

Note: Linux is NOT "eating" your RAM! Please take a look at Geirha's excellent answer below to understand why...

After the above note, if you still feel "cleaning" the cache could help, you can certainly try: it's a one-liner from the terminal:

sync && echo 3 | sudo tee /proc/sys/vm/drop_caches

There's no easy way to disable the cache, but you can achieve the same effect by cleaning it as often as every minute, if you want to:

  • Make it a cron-job

  • Press Alt-F2, type gksudo gedit /etc/crontab, and add this line near the bottom:

    */15 * * * * root sync && echo 3 > /proc/sys/vm/drop_caches

  • This cleans every 15 minutes. You can set to 1 or 5 minutes if you really want to by changing the first parameter to * or */5 instead of */15

One liner to know REAL free RAM, excepting cache

Geirha's answer explains the details, but in short, you get the number of free megabytes with:

free -m | sed -n -e '3p' | grep -Po "\d+$"

which on my 2GB command-line server returns an extremely health 1835.

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ish
  • 141,990
69

Help! Linux ate my RAM!

www.linuxatemyram.com explains this beautifully in FAQ form, with the essentials being:

What's going on?

Linux is borrowing unused memory for disk caching. This makes it looks like you are low on memory, but you are not! Everything is fine!

Why is it doing this?

Disk caching makes the system much faster! There are no downsides, except for confusing newbies. It does not take memory away from applications in any way, ever!

What if I want to run more applications?

If your applications want more memory, they just take back a chunk that the disk cache borrowed. Disk cache can always be given back to applications immediately! You are not low on ram!

How do I see how much free ram I really have?

To see how much ram your applications could use without swapping, run free -m and look at the "available" column: 

$ free -m
              total        used        free      shared  buff/cache   available
Mem:           1504        1491          13           0         855      792
Swap:          2047           6        2041
This is your answer in mebibytes.

Source: as mentioned, the excellent www.linuxatemyram.com -- please visit for more information.

geirha
  • 47,279
11

To Check your Current Memory Usage 

 watch -n 1 free -m

or

 watch -n 1 cat /proc/meminfo

To Free Up Space

 sudo sysctl -w vm.drop_caches=3

NOTE: this action won't make your system faster nor it will affect its stability and performance, it will just clean up memory used by the Linux Kernel on caches.

or 

 sudo sync && echo 3 | sudo tee /proc/sys/vm/drop_caches

NOTE: You can use cron jobs to schedule the commands above to run at specific time intervals.

SilleBille
  • 463
0

As we can see the cashing not a problem just if it cause swapping, what you can avoid by managing the vm.swappiness value. Maybe that's what you looking for: why-is-swap-being-used-even-though-i-have-plenty-of-free-ram

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Tamas
  • 9