From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41070) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XtyBM-0003RB-Ck for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:28:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XtyBH-0003TZ-U7 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:28:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36287) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XtyBH-0003TG-L4 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:28:19 -0500 Date: Thu, 27 Nov 2014 14:28:14 +0200 From: "Michael S. Tsirkin" Message-ID: <20141127122814.GA13476@redhat.com> References: <1417088742-4538-1-git-send-email-den@openvz.org> <1417088742-4538-3-git-send-email-den@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH 2/2] balloon: add a feature bit to let Guest OS deflate balloon on oom List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrey Korolyov Cc: "Denis V. Lunev" , "qemu-devel@nongnu.org" , Raushaniya Maksudova , Anthony Liguori On Thu, Nov 27, 2014 at 03:50:11PM +0400, Andrey Korolyov wrote: > On Thu, Nov 27, 2014 at 2:45 PM, 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. > > > > Signed-off-by: Denis V. Lunev > > CC: Raushaniya Maksudova > > CC: Anthony Liguori > > CC: Michael S. Tsirkin ... > Had you tried this with a system-wide OOM on a real workload? This > behavior can work perfectly with dedicated memory cgroups, but I`m > afraid it would be unusable when entire system stalls and waits for a > balloon deflation. That's really a question about guest drivers though, isn't it? So you aren't responding to correct patches, and aren't copying the correct people. -- MST