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

KY Srinivasan
2012-11-08T22:02:59Z

> -----Original Message-----
> From: David Rientjes [mailto:rientjes@google.com]
> Sent: Monday, November 05, 2012 5:33 PM
> To: KY Srinivasan
> Cc: Andrew Morton; Greg KH; olaf@aepfle.de; linux-kernel@vger.kernel.org;
> andi@firstfloor.org; apw@canonical.com; devel@linuxdriverproject.org; linux-
> mm@kvack.org; Hiroyuki Kamezawa; Michal Hocko; Johannes Weiner; Ying Han
> Subject: RE: [PATCH 1/2] mm: Export vm_committed_as
>
> 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.)

Yes, this makes sense. I just want to access (read) this metric. Andrew, if you are willing to
take this patch, I could send one.

Regards,

K. Y