Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756383AbdLVSHz (ORCPT ); Fri, 22 Dec 2017 13:07:55 -0500 Received: from omzsmtpe03.verizonbusiness.com ([199.249.25.208]:13898 "EHLO omzsmtpe03.verizonbusiness.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752549AbdLVSHv (ORCPT ); Fri, 22 Dec 2017 13:07:51 -0500 From: alexander.levin@verizon.com X-Host: surveyor.tdc.vzwcorp.com To: Michal Hocko CC: Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Shakeel Butt , Paolo Bonzini Subject: Re: [PATCH 4.14 108/159] kvm, mm: account kvm related kmem slabs to kmemcg Thread-Topic: [PATCH 4.14 108/159] kvm, mm: account kvm related kmem slabs to kmemcg Thread-Index: AQHTe0+366OaoPANA0qSyRlux92y3Q== Date: Fri, 22 Dec 2017 18:07:23 +0000 Message-ID: <20171222180720.mpc7ffshljrce4hf@sasha-lappy> References: <20171222084623.668990192@linuxfoundation.org> <20171222084629.570989756@linuxfoundation.org> <20171222093407.GN4831@dhcp22.suse.cz> <20171222124122.GA30743@kroah.com> <20171222130607.GQ4831@dhcp22.suse.cz> <20171222174002.6qiqllf3bhmjangn@sasha-lappy> <20171222175616.GS4831@dhcp22.suse.cz> In-Reply-To: <20171222175616.GS4831@dhcp22.suse.cz> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: NeoMutt/20170113 (1.7.2) x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.144.60.250] Content-Type: text/plain; charset="us-ascii" Content-ID: <4DEE3F789E98584DACA6A63231FDCC5B@vzwcorp.com> MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id vBMI80hP011176 Content-Length: 3877 Lines: 81 On Fri, Dec 22, 2017 at 06:56:16PM +0100, Michal Hocko wrote: >On Fri 22-12-17 17:40:10, Sasha Levin wrote: >> On Fri, Dec 22, 2017 at 02:06:07PM +0100, Michal Hocko wrote: >> >On Fri 22-12-17 13:41:22, Greg KH wrote: >> >> On Fri, Dec 22, 2017 at 10:34:07AM +0100, Michal Hocko wrote: >> >> > On Fri 22-12-17 09:46:33, Greg KH wrote: >> >> > > 4.14-stable review patch. If anyone has any objections, please let me know. >> >> > > >> >> > > ------------------ >> >> > > >> >> > > From: Shakeel Butt >> >> > > >> >> > > >> >> > > [ Upstream commit 46bea48ac241fe0b413805952dda74dd0c09ba8b ] >> >> > > >> >> > > The kvm slabs can consume a significant amount of system memory >> >> > > and indeed in our production environment we have observed that >> >> > > a lot of machines are spending significant amount of memory that >> >> > > can not be left as system memory overhead. Also the allocations >> >> > > from these slabs can be triggered directly by user space applications >> >> > > which has access to kvm and thus a buggy application can leak >> >> > > such memory. So, these caches should be accounted to kmemcg. >> >> > > >> >> > > Signed-off-by: Shakeel Butt >> >> > > Signed-off-by: Paolo Bonzini >> >> > > Signed-off-by: Sasha Levin >> >> > > Signed-off-by: Greg Kroah-Hartman >> >> > >> >> > The patch is not marked for stable, neither it fixes an existing bug. >> >> > It is a nice to have thing for sure but I am wondering how this got >> >> > through stable-filter. >> >> >> >> Sasha picked it out, and it seemed like a sane thing to backport. If >> >> you think it's not worthy, I'll gladly drop it, but it seemed like such >> >> a simple bugfix to include. >> > >> >It is not that I would have some specific concerns about this particular >> >patch. It is more of a worry about the overal process. I thought that >> >_any_ patch backported to the stable tree would require a specific bug >> >to be fixed or in exceptional cases a performance issue. I have >> >experienced this pushback myself when trying to push "no real bug report >> >but better to have this plugged" patches. >> > >> >So something has apparently changed in the process, I just haven't >> >noticed it. I am worried this might lead to more regression in future. >> >Not that my worry counts all that much as I am not a stable kernel user >> >though. So this is just my 2c worth of worry. >> >> The way I see it is that stable commits are supposed to fix a bug that >> a user can hit/exploit, it doesn't have to have an actual user >> complaining about it. >> >> For this particular commit, the way I read it is that a user can avoid >> his kmemcg limits (maybe maliciously), which would qualify as an >> actual bug we want to get fixed. > >How are you going to judge all the possible relations to other >subsystems? I mean there is a good reason maintainers mark patches for >stable trees. How do you want to competently decide this for them? Can >you do that for all subsystems? > >I do not want to underestimate your judgment or misinterpret your >process here but I _believe_ that picking patches based on the changelog >without a deep understanding of the subsystem is really risky. We do >not really have to go a long way to see that. Just look at other patch >in this very thread [1]. But maybe our our understanding of the stable >trees are different. I don't try and override maintainers, I mostly try to get fixes out of subsystems where maintainers/authors partially (or just don't) mark their commits for stable. These patches also go through a much longer review process than commits that are marked for stable (there are at least 3 emails issued for each such commit, and at least 1 week (usually much more) is given for reviews). -- Thanks, Sasha