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Message-ID: <20121106144644.GA29017@dhcp22.suse.cz>
Date: Tue, 6 Nov 2012 15:46:44 +0100
From: Michal Hocko <mhocko@...e.cz>
To: David Rientjes <rientjes@...gle.com>
Cc: KY Srinivasan <kys@...rosoft.com>,
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>,
Johannes Weiner <hannes@...xchg.org>,
Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 1/2] mm: Export vm_committed_as
On Mon 05-11-12 14:33:12, David Rientjes wrote:
> 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.
Agreed, we should rather make sure that nobody can manipulate the value
from modules.
> (And why percpu_counter_read_positive() returns a signed type is a
> mystery.)
Strange indeed. The last commit changed it from long to s64 to suport
values bigger than 2^31 but even the original long doesn't make much
sense to me.
--
Michal Hocko
SUSE Labs
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