I have a powerful server with 24GB of ram and an Intel Xenon quad core processor that I'm using to run a bunch of virtual machines for an office on using VirtualBox.

Lately there has been a problem though. If I run free this is what I get:


total used free shared buffers cached
Mem: 24733688 24531132 202556 0 79212 23492972
-/+ buffers/cache: 958948 23774740
Swap: 23437304 0 23437304



I have sysstat install so I ran sar -r on the command line and I found:


02:05:01 PM 19725876 5007812 20.25 309100 511408 4694764 9.75
02:15:01 PM 19725004 5008684 20.25 309352 511412 4697920 9.75
02:25:01 PM 19719736 5013952 20.27 309508 515608 4694840 9.75
02:35:01 PM 19708688 5025000 20.32 309696 520112 4701960 9.76
02:45:01 PM 215180 24518508 99.13 198292 19825416 4695892 9.75
02:55:01 PM 207744 24525944 99.16 198592 19833400 4695276 9.75
03:05:01 PM 200148 24533540 99.19 198904 19837592 4697116 9.75
03:15:01 PM 199720 24533968 99.19 199240 19837604 4700032 9.76


a little before 2:45 PM I had my RAM eaten. Going back through my brain I remember that at that time I ran the command VBoxManage clonehd XXXXX.vdi to clone one of my virtual hard drives.

I tried this again to make sure that the VBoxManage clonehd command was really the thing that was eating my RAM and it was. My question is - how do I reclaim the RAM. When the process that ate all the ram finished (I think it's the VBoxSVC process) it just leaves me with all my RAM used. How do I free up the RAM without restarting the server?

I'm running ubuntu 10.04 server as the OS

Thanks

Your RAM is fine, and it isn't being "eaten". If you look at the "Mem" line, you have 23,492,972 Kb Cached. This means that it was used at some point in time, and rather than writing zeros or ones back to it, what was put there is just kept there in case it is needed again. If something else needs to use the RAM, the oldest cached info will be overwritten by the new info.

HTH

Forrest

So I figured out something more about this. I went through the VBox.log file corresponding to the time I had the issue and I found many many lines similar to:


07:05:10.490 AssertLogRel /home/vbox/vbox-3.2.10/src/VBox/VMM/PGMSharedPage.cpp(155) VBOXSTRICTRC pgmR3SharedModuleRegRendezvous(VM*, VMCPU*, void*): RT_SUCCESS_NP(rc)
07:05:10.490 VERR_PGM_PHYS_INVALID_PAGE_ID (-1637) - Trying to free a page with an invalid Page ID.


I've never encountered a page fault before. What does this mean?

That's actually closer to a protection fault than a (normal) page fault. Happens. You might be surprised how many page faults you've actually encountered - even with all that RAM.

(Re-)read what forrestt said. Note that the kbcommit number has hardly changed - that means your "real" usage has hardly increased at all. Have a read of this.

Thanks for your help.

I think this "fault" might be coming from the pagefusion thing in virtualbox that is supposed to de-duplicate ram usage across multiple virtual machines of the same type. Why this is causing this VERR_PGM_PHYS_INVALID_PAGE_ID...???

I turned it off and the problem seemed to go away so far...

Any thoughts?

No idea, never even looked at it as I don't run Windoze guests. The Linux kernel offers its own memory de-dup these days if apps are smart enough to advise it that storage (ranges) is/are candidates. I did see a note on vbox-devl they weren't going in that direction (late last year).