Memory in openVZ – all you need to know

First, calculating memory

I want 1GB of ram, how many pages would those be ?
To calculate the numebrs for an openvz conf file, you should know that in container config files, the numbers there are pages, not bytes, you should probably know that a page of memory is 4k which is 4096 bytes

So a gigabyte is 1073741824 bytes

Number of pages = 1073741824 / 4096

So a gigabyte is 262144 pages (which open VZ should get in the config file to end up with a gigabyte of ram).

Now To what values in the openvz config file mean.

So, a memory block in oppenvz is measured by pages not bytes or megabytes, so the word pages generally means memory, now let us look at some variables in the openvz config file, vm means virtual machine (which is your container)

Values are specified in the form of
parameter=”barrier:limit”
For example
VMGUARPAGES=”67584:2147483647″

vmguarpages = VM Guaranteed Pages,┬áthe barrier is the effective number (The limit should be set to maximum integer, 2147483647 on 32bit and 9223372036854775807 on 64bit even though it is not defined or useful yet), If the current amount of allocated memory space does not exceed the guaranteed amount (the barrier of vmguarpages), memory allocations of container’s applications always succeed. If the current amount of allocated memory space exceeds the guarantee but below the barrier of privvmpages, allocations may or may not succeed, depending on the total amount of available memory in the system. if allocations exceed privvmpages, allocations will fail.
oomguarpages = Out Of Memory Guaranteed pages (Total for all machines should not exceed the available memory on the server) this is like the above, but assuming the system has no choice but to kill procesees, the system will weigh this in to chose what VM to kill from.
privvmpages = Private VM pages (The barrier and the limit of privvmpages parameter impose an upper limit on the memory allocations)

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