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

KY Srinivasan
2012-11-08T22:11:45Z

> -----Original Message-----
> From: Andrew Morton [mailto:akpm@linux-foundation.org]
> Sent: Thursday, November 08, 2012 5:05 PM
> To: KY Srinivasan
> Cc: David Rientjes; 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 Thu, 8 Nov 2012 22:01:33 +0000
> KY Srinivasan <kys@microsoft.com> wrote:
>
> >
> >
> > > -----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.
>
> Sure. I suppose that's better, although any module which modifies
> committed_as would never pass review (rofl).

Thanks Andrew; I will send the patch out along with the appropriately modified balloon driver patch.

Regards,

K. Y
>
>