On Thu, Aug 8, 2013 at 9:39 AM, Martin Kletzander <mkletzan@xxxxxxxxxx> wrote: > At first let me explain that libvirt is not ignoring the cache=none. > This is propagated to qemu as a parameter for it's disk. From qemu's > POV (anyone feel free to correct me if I'm mistaken) this means the file > is opened with O_DIRECT flag; and from the open(2) manual, the O_DIRECT > means "Try to minimize cache effects of the I/O to and from this > file...", that doesn't necessarily mean there is no cache at all. Thanks for explanation. > But even if it does, this applies to files used as disks, but those > disks are not the only files the process is using. You can check what > othe files the process has mapped, opened etc. from the '/proc' > filesystem or using the 'lsof' utility. All the other files can (and > probably will) take some cache and there is nothing wrong with that. In my case there was 4GB of caches. Just now, I have thrashed one instance with many read/writes on various devices. In total, tens of GB of data. But the cache (on host) did not grow beyond 3MB. I'm not yet able to reproduce the problem. > Are you trying to resolve an issue or asking just out of curiosity? > Because this is wanted behavior and there should be no need for anyone > to minimize this. Once or twice, one of our VMs was OOM killed because it reached 1.5 * memory limit for its cgroup. Here is an 8GB, instance. Libvirt created cgroup with 12.3GB memory limit, which we have filled to 98% [root@dev-cmp08 ~]# cgget -r memory.limit_in_bytes -r memory.usage_in_bytes libvirt/qemu/i-000009fa libvirt/qemu/i-000009fa: memory.limit_in_bytes: 13215727616 memory.usage_in_bytes: 12998287360 The 4G difference is the cache. That's why I'm so interested in what is consuming the cache on a VM which should be caching in guest only. Regards, Brano Zarnovican _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
