linux-kernel - Re: [PATCH 1/2] mm: Export vm_committed

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Message-Id: <20121108140529.af7849c8.akpm@linux-foundation.org>
Date:	Thu, 8 Nov 2012 14:05:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 1/2] mm: Export vm_committed_as

On Thu, 8 Nov 2012 22:01:33 +0000
KY Srinivasan <kys@...rosoft.com> wrote:

> 
> 
> > -----Original Message-----
> > From: David Rientjes [mailto:rientjes@...gle.com]
> > Sent: Monday, November 05, 2012 5:33 PM
> > To: KY Srinivasan
> > Cc: Andrew Morton; Greg KH; olaf@...fle.de; linux-kernel@...r.kernel.org;
> > andi@...stfloor.org; apw@...onical.com; devel@...uxdriverproject.org; linux-
> > mm@...ck.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).

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