From: KY Srinivasan <kys@microsoft.com>
To: Michal Hocko <mhocko@suse.cz>
CC: Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "andi@firstfloor.org" <andi@firstfloor.org>,
        "apw@canonical.com" <apw@canonical.com>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Ying Han <yinghan@google.com>
Subject: RE: [PATCH 1/2] mm: Export vm_committed_as
Thread-Topic: [PATCH 1/2] mm: Export vm_committed_as
Thread-Index: AQHNpOUVxeGuP2ksmkqoWwiw1ukrt5eukjYAgAAumACAAKkDgIAB+liAgCbqv6CAA6TlAIAAA/OAgAC6PYCAAD7C0A==
Date: Tue, 6 Nov 2012 12:53:01 +0000
Message-ID: <426367E2313C2449837CD2DE46E7EAF930DFBA2F@SN2PRD0310MB382.namprd03.prod.outlook.com>
References: <1349654347-18337-1-git-send-email-kys@microsoft.com>
 <1349654386-18378-1-git-send-email-kys@microsoft.com>
 <20121008004358.GA12342@kroah.com>
 <426367E2313C2449837CD2DE46E7EAF930A1FB31@SN2PRD0310MB382.namprd03.prod.outlook.com>
 <20121008133539.GA15490@kroah.com>
 <20121009124755.ce1087b4.akpm@linux-foundation.org>
 <426367E2313C2449837CD2DE46E7EAF930DF7FBB@SN2PRD0310MB382.namprd03.prod.outlook.com>
 <20121105134456.f655b85a.akpm@linux-foundation.org>
 <426367E2313C2449837CD2DE46E7EAF930DFA7B8@SN2PRD0310MB382.namprd03.prod.outlook.com>
 <20121106090539.GB21167@dhcp22.suse.cz>
In-Reply-To: <20121106090539.GB21167@dhcp22.suse.cz>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3790
Lines: 93


> -----Original Message-----
> From: Michal Hocko [mailto:mstsxfx@gmail.com] On Behalf Of Michal Hocko
> Sent: Tuesday, November 06, 2012 4:06 AM
> 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; Johannes Weiner; Ying Han
> Subject: Re: [PATCH 1/2] mm: Export vm_committed_as
> 
> On Mon 05-11-12 22:12:25, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: Andrew Morton [mailto:akpm@linux-foundation.org]
> > > Sent: Monday, November 05, 2012 4:45 PM
> > > To: KY Srinivasan
> > > Cc: 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 Sat, 3 Nov 2012 14:09:38 +0000
> > > KY Srinivasan <kys@microsoft.com> wrote:
> > >
> > > >
> > > >
> > > > > >
> > > > > > Ok, but you're going to have to get the -mm developers to agree that
> > > > > > this is ok before I can accept it.
> > > > >
> > > > > Well I guess it won't kill us.
> > > >
> > > > Andrew,
> > > >
> > > > I presumed this was an Ack from you with regards to exporting the
> > > > symbol. Looks like Greg is waiting to hear from you before he can check
> > > > these patches in. Could you provide an explicit Ack.
> > > >
> > >
> > > Well, I do have some qualms about exporting vm_committed_as to modules.
> > >
> > > vm_committed_as is a global thing and only really makes sense in a
> > > non-containerised system.  If the application is running within a
> > > memory cgroup then vm_enough_memory() and the global overcommit
> policy
> > > are at best irrelevant and misleading.
> > >
> > > If use of vm_committed_as is indeed a bad thing, then exporting it to
> > > modules might increase the amount of badness in the kernel.
> > >
> > >
> > > I don't think these qualms are serious enough to stand in the way of
> > > this patch, but I'd be interested in hearing the memcg developers'
> > > thoughts on the matter?
> > >
> > >
> > > Perhaps you could provide a detailed description of why your module
> > > actually needs this?  Precisely what information is it looking for
> > > and why?  If we know that then perhaps a more comfortable alternative
> > > can be found.
> >
> > 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.
> 
> So IIUC it will be guest who reports the value and the guest runs in the
> ring-0 so it is not in any user process context, right?
> If this is correct then memcg doesn't play any role here.

Thanks Michal. Yes, the kernel driver reports this metric to the host.
Andrew, let me know how I should proceed here.

Thanks,

K. Y


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/