RE: [PATCH 1/2] mm: Export vm_committed_as

David Rientjes
2012-11-05T22:33:20Z

On Mon, 5 Nov 2012, KY Srinivasan wrote:

> The Hyper-V host has a policy engine for managing available physical memory across
> competing virtual machines. This policy decision is based on a number of parameters
> including the memory pressure reported by the guest. Currently, the pressure calculation is
> based on the memory commitment made by the guest. From what I can tell, the ratio of
> currently allocated physical memory to the current memory commitment made by the guest
> (vm_committed_as) is used as one of the parameters in making the memory balancing decision on
> the host. This is what Windows guests report to the host. So, I need some measure of memory
> commitments made by the Linux guest. This is the reason I want export vm_committed_as.
>

I don't think you should export the symbol itself to modules but rather a
helper function that returns s64 that just wraps
percpu_counter_read_positive() which your driver could use instead.

(And why percpu_counter_read_positive() returns a signed type is a
mystery.)