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Is privvmpages's MAX limited to the amount of RAM on a computer [message #35014]

Fri, 20 February 2009 00:02

CatDaaaady
Messages: 7
Registered: September 2008
Location: 94555

Junior Member

I can't seem to get a straight answer on this one.
After reading these links:
http://forum.openvz.org/index.php?t=msg&goto=2594&#m sg_2886
http://maxgarrick.com/understanding-openvz-resource-limits/
http://forum.openvz.org/index.php?t=msg&goto=32000&
http://wiki.openvz.org/Privvmpages#privvmpages
http://download.openvz.org/doc/OpenVZ-Users-Guide.pdf

I am unsure if we can set a VE's privvmpages to more than a system's total RAM.

For instance if I have a system that has:
4GB RAM
4GB SWAP

*HardwareNode*
free -m
             total       used       free     shared    buffers     cached
Mem:          3926        224       3702          0          4         78
-/+ buffers/cache:        141       3785
Swap:         4094          9       4085

I can run this command.
vzctl set 33503 --privvmpages 4G --save
Then run "free -m" inside the VE and we will see 4Gs for the system.

*VE*
$ free -m
             total       used       free     shared    buffers     cached
Mem:          3926         75       3850          0          0          0
-/+ buffers/cache:         75       3850
Swap:            0          0          0
$

But if I set it to more then 4G it will not show up as system memory.
vzctl set 33503 --privvmpages 6G --save

*VE*
$ free -m
             total       used       free     shared    buffers     cached
Mem:          3926         75       3850          0          0          0
-/+ buffers/cache:         75       3850
Swap:            0          0          0
$

Thoughts?
If the answer is "no". My follow up question is "Why not? Assuming you have enough SWAP to cover it." Smile

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Re: Is privvmpages's MAX limited to the amount of RAM on a computer [message #35015 is a reply to message #35014]

Fri, 20 February 2009 00:13

CatDaaaady
Messages: 7
Registered: September 2008
Location: 94555

Junior Member

Also I read this.
http://forum.parallels.com/showthread.php?t=59082

But I am still unsure. Smile

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Re: Is privvmpages's MAX limited to the amount of RAM on a computer [message #35022 is a reply to message #35015]

Fri, 20 February 2009 19:04

CatDaaaady
Messages: 7
Registered: September 2008
Location: 94555

Junior Member

Another interesting note.
I created some code to malloc and take up about 2G worth of memory.
I set the VE to 4G of memory to match the RAM on the hardware node.
Then I run the program. As you can see below I can only run the program 2 times before I get a malloc error.
vzctl set 33503 --privvmpages 4G

*Inside the VE*

$  free -m
             total       used       free     shared    buffers     cached
Mem:          3926         73       3853          0          0          0
-/+ buffers/cache:         73       3853
Swap:            0          0          0
$


$ ./allocateandfill &
[1] 32375
$ ./allocateandfill &
[2] 32376
$ Success
./allocateandfill &
[3] 32377
$ malloc: Cannot allocate memory

$  free -m
             total       used       free     shared    buffers     cached
Mem:          3926       3926          0          0          0          0
-/+ buffers/cache:       3926          0
Swap:            0          0          0
$

So the above error is expected.

Then I set the VE to something over the amount of physical ram on the hardware node...
vzctl set 33503 --privvmpages 6G

*Inside the VE*
$ free -m
             total       used       free     shared    buffers     cached
Mem:          3926         73       3853          0          0          0
-/+ buffers/cache:         73       3853
Swap:            0          0          0
$

NOTICE no change in the total memory!!?!!

$  ./allocateandfill &
[1] 32483
$  ./allocateandfill &
[2] 32484
$  ./allocateandfill &
[3] 32485
$

NOTICE no errors!

$ free -m
             total       used       free     shared    buffers     cached
Mem:          3926       3926          0          0          0          0
-/+ buffers/cache:       3926          0
Swap:            0          0          0
$

Memory is totally used up. And it shows just 4Gs. "top" shows the same.

*On the Hardware node*
free -m
             total       used       free     shared    buffers     cached
Mem:          3926       3810        116          0          0          8
-/+ buffers/cache:       3800        125
Swap:         4094       1678       2415

Notice the hardware node is using all its ram and half the swap. As expected. It needs to grab 6G from somewhere.

So my question: What's up? Why does the VE not show all the memory it has available to it???

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