Xen memory balloon driver

Create the domu with minimum memory equal to maximum memory so the balloon driver is never called. Set the balloon driver s target to the desired amount of ram. Ballooning is more than enough to do memory overcommit on xen. Ballooning is an activity that happens when the esxi host is running out of physical memory. When ballooning out allocating memory to return to xen we dont really want the kernel. To deflate the balloon, the balloon driver will choose one of the pages on its list that it has allocated, and then asks xen to put some memory behind the gpfn.

Linux kernel documentation abi stable sysfsdevices. The machine pages backing this memory can then be reclaimed by xen dom0. Device drivers xen driver support xen memory balloon driver. Memory overcommit provides the ability for the sum of the physical memory. Such a driver exists in xen, and was considered for virtio, but seems to have been. The greater the difference between the values for maximum memory and available memory, the longer it takes to boot pvhvm guests. Systems and more creating a driver for selfballooning a virtio. The hypervisor will detect what memory the balloon driver has reclaimed and will free it up on the host physical memory layer. Especially, we are going to show you how much fun it is to work with xen hosts and domus and setting up a funtoo xen server without general clicky guis or other frontends. It should be onlined by user through standard sysfs interface. If xen determines that the guest is allowed to increase its memory, and there is free memory available, then it will allocate an mfn and put it in the p2m table behing that gpfn.

As you may know, ballooning is a technique used to dynamically adjust the physical memory in use by a guest. Ballooning is a process where the esxi host reclaims memory back from the virtual machine. If the memory usage value is high, and the host has high ballooning or swapping, check the amount of free physical memory on the host. If you are upgrading domain 0 linux kernel from a nonpvops classic, 2. While contentbased pagesharing, vmmbased demand paging, and hotplug memory are all glamorous mechanisms that can be used to improve memory efficiency, the simple existing balloon driver provided by xen, when combined with graybox data collected by a few scripts, is sufficient to implement reasonable memory overcommit.

This means all guests including dom0 are equal, and get the same amount of cpu time. The balloon driver allows the xen domain to request more memory from the system to expand the domains memory allocation, or alternatively return unneeded memory to the system. From the kernels perspective, however, that memory is still part of the system and is being used by the balloon driver. As a result, the boot time for the virtual machine takes longer than expected. Vmware, virtualbox, xen and other hypervisor systems try to utilize the. If the active memory is consistently low, the memory size might be too large. The ballooning driver does not support hugepages, so keep the memory of the domu constant. Thu, 04 jun if this were instead allocate on demandwhere you actually allocated the memory from xen when you hit an xen balloon entry, there would be a risk that the memory you needed to boot until the balloon driver could run would already have been allocated to a different domain. The balloon driver can then safely return that memory to xen, so the domain has been shrunk. Either with the mechanism provided by your toolstack or directly with xxx is the amount of ram in kib. This patch to the balloon driver eliminates the need for a userspace program to slosh memory between domains and xen. Verify memory balloon driver status of virtual machine. Pvhvm hardwareassisted virtualization with paravirtualized drivers in.

The method is called memory ballooning 1, 2, and it must be supported by the guest operating system to work. In vmware esx and esxi if you install vmware tools, those will enable the memory management driver aka balloon driver. Unfortunately, the balloon driver is unaware of memory pages locked by other processes. Xen is a native, or baremetal, hypervisor that allows multiple distinct virtual machines referred to as domains to share a single physical machine. Ballooning, rebooting, and the feature youve never heard of xen. For x86 architectures traditional device model device emulator based on xen fork of qemu qemu upstream device model device emulator based on upstream qemu default, unless stubdomains are used default, unless stubdomains are used. Ballooning is more than enough to do memory overcommit on. Vm memory ballooning can create performance problems. The balloon driver allows memory to be dynamically added or removed from the domain, in order to allow host memory to be balanced between multiple domains. Xen memory management on small server server fault. When the hypervisor is running low on memory it sets a target page size and the balloon driver will then inflate, creating artificial memory pressure within the vm, causing the operating system to either pin memory. Vmware tools is required to be uptodate for the memory balloon driver vmmemctl to operate properly.

If the guest memory balloon driver does not free sufficient memory to reach its target, the guest will proceed to run with a nonzero number of outstanding pod pages. The current number of times that the balloon driver has attempted to increase the size of the balloon. The missing memory is due to a red hat balloon driver bug 1437309 which was fixed in red hat 7. Xen does have dynamic memory management techinques, namely ballooning and selfballooning. When memory pressure changes, the balloon is expected to change size. Oct 31, 2014 when a balloon driver inflates to the point where the vm no longer has enough memory to run its processes within itself, it starts using another vm memory technique known as memory swapping. This patch introduces the xen balloon driver, though it currently only. When ballooning out allocating memory to return to xen we dont really want the kernel to try too hard since that can trigger the oom killer. When xen sees that the pod entry, it will take an mfn from the pod pool and put it in the p2m for that gpfn. In libvirt, memory allocation and hence the ballooning capability for a guest can be configured using the memory, currentmemory and memballoon tags. Memory overcommitment in xenserver and esx speakvirtual. Drivers should be signed for windows 64bit platforms. Ballooning is achieved via a device driver balloon driver included by default with every installation of vmware tools.

When a balloon driver inflates to the point where the vm no longer has enough memory to run its processes within itself, it starts using another vm memory technique. Xen dom0 controls the balloon module running within solaris guest, directing it to allocate guest pages and pin them in physical memory. How to know if the balloon driver is running mailing list archive. Vmware tools status can be found from the summary tab of the virtual machine or go to the host and.

You can adjust memory allocation per domain using xl memset. Xen balloon driver enables returningclaiming memory tofrom xen. Code signing drivers for the windows 64bit platforms. Xen balloon driver gets its page directly from page. Set the amount of memory dom0 is given at boot time. As the highest privilege process on the system, xen is responsible for the distribution of processor and memory resources between guest domains on the host. The driver uses a proprietary ballooning technique that provides predictable performance that closely matches the behavior of a native system under similar memory constraints. The balloon fills the rest of the memory and gives it back to the host for the host to use elsewhere. This is a known bug in vmware tools and also openvmtools. Vmware kb 1003586 as the zing java virtual machine zvm is using locked memory pages provided by the zing system tools zst and the balloon driver is ignoring them, wrong assumptions are made over. Why does balloon driver think that only 1064 kib is free. It does not support memory overcommit, in that it does not allow vms to actually use more memory than what you have physically available in your system said another way.

Never execute the xl memset command against the domu to change its memory size. Recommended base configuration for xen host support suse. When read it reports memory the domain owns in bytes. If your distribution does not provide binary drivers for windows, you can use the package from the fedora project. This configuration causes the xen balloon driver to shrink the guest memory to the target size. If the active memory size is the same as the granted memory size, the demand for memory is greater than the memory resources available. You can maximize performances by using virtio drivers. The availability and status of the virtio drivers depends on the guest os and platform. Ballooncompactioninfrastructurecanmigrateballoonedpagesfromstart of linux memory zone to end of zone, hence creating contiguous guest physicaladdressspace. Set the balloon drivers target to the desired amount of ram.

Another mechanism to allow memory overcommitment is the swappingpaging at the esxesxi level, but this is extremely slow and you should avoid it. Kvm and xen provide a method to change the amount of memory in use by guests at runtime. Iirc the core balloon driver is always present when xen is enabled and so the kernel will respond to requests from the hosttoolstack to change the amount of ram e. It should be mentioned that hotplugged memory is not onlined automatically. Funtoo xen fun we are talking about xen on funtoo linux and how to setup xen virtualization properly. Vmware tools status can be found from the summary tab of the virtual machine or go to the host and click on virtual machines tab to see the status of. The memory balloon driver vmmemctl collaborates with the server to reclaim pages that are considered least valuable by the guest operating system. The balloon driver requests memory from the system allocator which it then directly gives back to xen. When you grow the domain again, the balloon driver retrieves memory from xen, and then frees it back to the guest.

Vmmemctl is the balloon driver which is responsible to perform one of the memory management techniques memory ballooning in esxesxi hosts. Xenusers domu max memory problem, pavel krejca balloon. Kernel memory allocation will be requested from the available memory for that vps, and cannot be paged out to swap. These drivers are digitally signed, and will work on 64bit versions of windows. Jul 17, 2010 maxmemory or just is the memory allocated at boot time to a guest. The balloon driver is used to adjust current memory reservation for solaris domu that is running on xen hypervisor. The demand of the virtual machine is too high for the host to handle. When dom0 the xen serverhypervisor needs more memory, and wishes to claim some from the guest vps domu, it asks the guest vpss balloon driver to inflate itself by asking its linux kernel for some memory.

This will slow down the vm, depending upon the amount of memory to recoup andor the quality of the storage iops delivered to it. When the guest or management toolstack touches such a page, the hypervisor would search the guest memory for a page containing only zeroes. As a result, the boot time for the virtual machine takes longer than. Oct 18, 2017 ballooning is a process where the esxi host reclaims memory back from the virtual machine. The kernel thinks that the balloon driver has allocated loads of memory, whereas actually that memory is not there anymore. Prevent the balloon driver from changing the memory reservation. The balloon driver will inflate and because it is inside the operating system it will start by getting memory from the free list. The balloon driver can inflate up to a maximum of 65%.