[Engine-devel] What BlockMigrationOnSwapUsagePercentage

Itamar Heim iheim at redhat.com
Thu Jun 14 14:21:45 UTC 2012


On 06/14/2012 04:59 PM, Mark Wu wrote:
> Hi guys
>
> I got the following error message when I tried to run a VM:
>
> "VM's swap percentage is above the threshold. (check your configuration
> parameters for Host Swap Percentage)."
>
> After increasing the parameter BlockMigrationOnSwapUsagePercentage, the
> problem disappeared.
>
> But I don't understand the logic here:
> IsVMSwapValueLegal
> ....
> return ((swap_total - swap_free - mem_available) * 100 /

analyzing this...
how much memory swap has
minus
how much is still available
gives the amount of swap used
then subtract the amount of RAM available - since it won't require swap 
for that amount of RAM.

that's gives how much swap is used (taking into consideration available 
RAM) as a percentage from physical memory

yes, could be written in a more readable way.

> physical_mem_mb) <= Config
> .<Integer> GetValue(ConfigValues.BlockMigrationOnSwapUsagePercentage);
>
>
> So anyone can help me explain it? Thanks a lot!
>
> Mark.
>
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