5a10b7dbf9
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 some memory at the last moment before some process will be 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. Allocate virtio feature bit for this: it is not set by default, the the guest will not deflate virtio balloon on OOM without explicit permission from host. Signed-off-by: Raushaniya Maksudova <rmaksudova@parallels.com> Signed-off-by: Denis V. Lunev <den@openvz.org> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> |
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