From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50607) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Gol-0003fr-Kt for qemu-devel@nongnu.org; Tue, 23 Jun 2015 01:32:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z7Goi-0000H3-DL for qemu-devel@nongnu.org; Tue, 23 Jun 2015 01:32:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45668) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Goi-0000Gx-5z for qemu-devel@nongnu.org; Tue, 23 Jun 2015 01:32:16 -0400 Date: Tue, 23 Jun 2015 07:32:12 +0200 From: "Michael S. Tsirkin" Message-ID: <20150623073159-mutt-send-email-mst@redhat.com> References: <1434365572-28381-1-git-send-email-den@openvz.org> <55880612.4050205@openvz.org> <1435007388.2237.132.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1435007388.2237.132.camel@HansenPartnership.com> Subject: Re: [Qemu-devel] [PATCH v7 0/1] balloon: add a feature bit to let Guest OS deflate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: James Bottomley Cc: "Denis V. Lunev" , qemu-devel@nongnu.org, Raushaniya Maksudova , Anthony Liguori On Mon, Jun 22, 2015 at 02:09:48PM -0700, James Bottomley wrote: > On Mon, 2015-06-22 at 15:56 +0300, Denis V. Lunev wrote: > > On 15/06/15 13:52, Denis V. Lunev wrote: > > > Excessive virtio_balloon inflation can cause invocation of OOM-killer, > > > when Linux is under severe memory pressure. Various mechanisms are > > > responsible for correct virtio_balloon memory management. Nevertheless it > > > is often the case that these control tools does not have enough time to > > > react on fast changing memory load. As a result OS runs out of memory and > > > invokes OOM-killer. The balancing of memory by use of the virtio balloon > > > should not cause the termination of processes while there are pages in the > > > balloon. Now there is no way for virtio balloon driver to free memory at > > > the last moment before some process get killed by OOM-killer. > > > > > > This does not provide a security breach as balloon itself is running > > > inside Guest OS and is working in the cooperation with the host. Thus > > > some improvements from Guest side should be considered as normal. > > > > > > To solve the problem, introduce a virtio_balloon callback which is > > > expected to be called from the oom notifier call chain in out_of_memory() > > > function. If virtio balloon could release some memory, it will make the > > > system to return and retry the allocation that forced the out of memory > > > killer to run. > > > > > > This behavior should be enabled if and only if appropriate feature bit > > > is set on the device. It is off by default. > > > > > > This functionality was recently merged into vanilla Linux (actually in > > > linux-next at the moment) > > > > > > commit 5a10b7dbf904bfe01bb9fcc6298f7df09eed77d5 > > > Author: Raushaniya Maksudova > > > Date: Mon Nov 10 09:36:29 2014 +1030 > > > > > > This patch adds respective control bits into QEMU. It introduces > > > deflate-on-oom option for baloon device which do the trick. > > > > > > Changes from v6: > > > - ported to virtio_add_feature > > > > > > Changes from v5: > > > - ported to QEMU current > > > > > > Changes from v4: > > > - spelling corrected according to suggestions from Eric Blake > > > > > > Changes from v3: > > > - ported to git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git tags/for_upstream_rebased > > > > > > Changes from v2: > > > - fixed mistake with bit number in virtio_balloon_get_features > > > > > > Changes from v1: > > > - From: in patch 1 according to the original ownership > > > - feature processing in patch 2 as suggested by Michael. It could be done > > > without additional field, but this will require to move the property > > > level up, i.e. to PCI & CCW level. > > > > > > Signed-off-by: Raushaniya Maksudova > > > Signed-off-by: Denis V. Lunev > > > CC: Anthony Liguori > > > CC: Michael S. Tsirkin > > > > > > P.S. Sorry for resend (if you have caught additional patch), I have > > > expirienced some troubles in the process > > > > > ping > > We seem to have become bogged down in a dispute over whether this flag > should be automatically enabled or disabled. To be honest, we don't > care, since we're going to be shipping qemu configured according to our > requirements (as are most other distros anyway). > > However, for the sake of getting the patch in, what about putting it in > as is (default disable) because that has no impact to the status quo. > If it later turns out everyone ships in a default enabled configuration, > why then someone can patch upstream qemu to match. > > James > Great, so I get your ack on it?