Cache Memory NEVER Released

[maraschin]

Hi,

I'm having a strange problem with all my computers that are running ubuntu...
After I do a lot of operations with files (like copy, compilation, etc), anything that makes use of the cache, makes the computer ran out of memory!
Well, I do not get any error! It will just not let me open any new applications...

Here an example that just happen:
I did compile a big project with Maven2 which downloaded a lot of files... Right now I get that my computer is using 72% as cache and 22% by programs... (By the way, I've 3GB of memory in this machine).

All seems fine, at least with the open applications like firefox that I'm using to write this new thread. The problem now is that I can't open any new applications, and that includes a simple terminal window!
Nothing that is not in memory already will start!

Does anyone knows for how long the cache system keeps the allocated memory?
Is there a way to make it release it back?

The compilation has ended for quite some time, all the files have already been written to the disc and I still don't have my memory back...
The only solution is to restart the machine.

I'm having the same problem with other machines that are running ubuntu too. All with 8.04 with the latest updates...

Any suggestions?
Any know Bugs???

BTW, I've been "googling" and searching in the forum but I did not find anything like it...

Regards,

/Carlo

[maraschin]

By the way, I ran free -m in a terminal window that was open before I ran out of memory...

free -m
total used free shared buffers cached
Mem: 3026 2809 217 0 290 1785
-/+ buffers/cache: 733 2293
Swap: 3922 0 3921

[rebeldevel]

That's true. I think Ubuntu should release some cache in a timely fashion, to avoid using swap.

EDIT: by the way, to free up cache memory, run this command:

sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"

[Mecharuva]

That's true. I think Ubuntu should release some cache in a timely fashion, to avoid using swap.

EDIT: by the way, to free up cache memory, run this command:

sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"

Awesome, I've been looking for this.
I just made a launcher for it on the desktop :]
Many thanks.

[sdennie]

The only thing dropping the cache will do is make your system a lot less responsive. If you want to avoid using swap while retaining the cache, add the following to /etc/sysctl.conf:

vm.swappiness = 1

Then run:

sudo sysctl -p

That change will stick over reboots.

[maraschin]

That's true. I think Ubuntu should release some cache in a timely fashion, to avoid using swap.

EDIT: by the way, to free up cache memory, run this command:

sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"

Thanks!
The command you sent did the trick!
( sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches" )

The scenario this time was that I just downloaded 2 iso files (LinuxMCE) and were using the computer normally to write the CDs, surfing and so on... The cache filled up and I was left without memory to open any new applications...

Kernel automatically releasing cache?
Nop, the swap wasn't even used and it did not released anything from the cache...
About future use of the cache:
Yes, I do want to use the cache now and than but in this scenario cache wasn't important...

[sdennie]

Thanks!
The command you sent did the trick!
( sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches" )

The scenario this time was that I just downloaded 2 iso files (LinuxMCE) and were using the computer normally to write the CDs, surfing and so on... The cache filled up and I was left without memory to open any new applications...

Kernel automatically releasing cache?
Nop, the swap wasn't even used and it did not released anything from the cache...
About future use of the cache:
Yes, I do want to use the cache now and than but in this scenario cache wasn't important...

Unless you've done something very odd to your machine, it's simply not possible that the cache is causing this. My guess is that nearly every person posting on this forum would find that if they did a "free -m" they would see that the cache is taking all available memory and yet none of them are having the problems you are describing. Something else must be going on. You are certainly free to run your machine however you see fit, but, by constantly dropping the cache, you are doing yourself a disservice.

[dnegorov]

I have the same problem with OpenSUSE 11.0

[maraschin]

I guess I did not google enough...

I found a "possible" solution...

http://www.faqs.org/docs/linux_admin/buffer-cache.html

The command sync may be the answer but I could not replicate it yet in my tests... it could be that update had crashed but I'm not sure.

I tried to fill up the cache and clean with sync and it seems to work fine. But even when I'd the cache full I still could open applications so I'll have to wait to try this one out when I get the same problem again and see if isn't another problem...

[sdennie]

This can't be a problem with the cache. Having your otherwise unused memory filled by the cache is a very good thing and dramatically improves system performance. If your applications need memory, linux will drop pages from the cache to make room for your applications. I suspect something else is going on here.