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Hi, I have an instance with 8G ram assigned. All block devices have cache disabled (cache=none) on host. However, cgroup is reporting 4G of cache associated to the instance (on host) # cgget -r memory.stat libvirt/qemu/i-000009fa libvirt/qemu/i-000009fa: memory.stat: cache 4318011392 rss 8676360192 ... When I drop all system caches on host.. # echo 3 > /proc/sys/vm/drop_caches # ..cache associated to the instance drops too. # cgget -r memory.stat libvirt/qemu/i-000009fa libvirt/qemu/i-000009fa: memory.stat: cache 122...

...07/2013 02:24 PM, Brano Zarnovican wrote: > Hi, > > I have an instance with 8G ram assigned. All block devices have cache > disabled (cache=none) on host. However, cgroup is reporting 4G of > cache associated to the instance (on host) > > # cgget -r memory.stat libvirt/qemu/i-000009fa > libvirt/qemu/i-000009fa: > memory.stat: cache 4318011392 > rss 8676360192 > ... > > When I drop all system caches on host.. > > # echo 3 > /proc/sys/vm/drop_caches > # > > ..cache associated to the instance drops too. > > # cgget -r memory.stat libvir...

...is. 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

...ted cgroup with 12.3GB memory > limit, which we have filled to 98% > The more it's filled with caches, the better, but if none of those are caches, whoa!, the limit should be increased. > [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 > You can get rid of these problems by setting your own memory limits. The defaults limit get set only if there is no <memtune> setting in the domain XML: http://libvirt.org/form...