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

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Date:	Mon, 5 Nov 2012 14:33:12 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KY Srinivasan <kys@...rosoft.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 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.)
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