# Calculating memory used by Xen hypervisor **URL:** \ **Category:** SLES Virtualization\ **Created:** [October 22, 2011, 12:46am UTC](https://forums.suse.com/t/calculating-memory-used-by-xen-hypervisor/22063 "2011-10-22T00:46:02Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![System1](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@System1](https://forums.suse.com/u/System1)\ **Post date:** [October 22, 2011, 12:46am UTC](https://forums.suse.com/t/calculating-memory-used-by-xen-hypervisor/22063/1 "2011-10-22T00:46:02Z")
According to ‘TID 3559698 - XEN Dom0 becomes unresponsive when shutting down a domU virtual machine’ ([http://www.novell.com/support/php/search.do?cmd=displayKC&docType=kc&externalId=3559698&sliceId=1&docTypeID=DT\_TID\_1\_1&dialogID=275099292&stateId=0%200%20275097402](http://www.novell.com/support/php/search.do?cmd=displayKC&docType=kc&externalId=3559698&sliceId=1&docTypeID=DT_TID_1_1&dialogID=275099292&stateId=0%200%20275097402)), I should be able to calculate approximately how much memory is used/needed by the Xen hypervisor.\> it is possible to get a good idea of how much is required by booting XEN[color=blue] > in the default configuration (all available memory assigned to dom0). > In this configuration, the total system memory minus the amount of > memory assigned to dom0 equals the amount required by the hypervisor.[/color] > With -only Dom0 running-, I see: ## Code: ## server:~ # xm info host : server release : 2.6.32.45-0.3-xen version : #1 SMP 2011-08-22 10:12:58 +0200 machine : x86\_64 total\_memory : 6143 free\_memory : 3592 max\_free\_memory : 5557 max\_para\_memory : 5553 max\_hvm\_memory : 5532 According to the TID\> The amount of memory needed by the hypervisor, domain0, and each domU[color=blue] > varies based on machine specifications, type of VM, etc. Therefore, > there are no fixed values that can be assigned to any of those > variables. However, ‘xm info’ can provide a view into the current state > of the system. There are 5 fields in the list that provide information > about the memory status: > > total\_memory : 6143 # Total RAM available to the system > free\_memory : 3592 # Free RAM (not in use by hypervisor, dom0, or any > domU) > max\_free\_memory : 5557 # Maximum value possible for"free\_memory" after > ballooning dom0 > max\_para\_memory : 5553 # Maximum amount of memory that could be > assigned to a new pv guest > max\_hvm\_memory : 5532 # Maximum amount of memory that could be assigned > to a new fv guest > [/color] > Dom0 has 2477 MB of memory assigned as can be seen here: ## Code: ## server:~ # xm list -l Domain-0 (domain (domid 0) (cpu\_weight 256) (cpu\_cap 0) (pool\_name Pool-0) (bootloader ) (vcpus 4) (cpus ((0 1 2 3) (0 1 2 3) (0 1 2 3) (0 1 2 3))) (on\_poweroff destroy) (description ) (on\_crash restart) (uuid 00000000-0000-0000-0000-000000000000) (bootloader\_args ) (name Domain-0) (on\_reboot restart) (maxmem 16777215) _(memory 2477)_ (shadow\_memory 0) (features ) (on\_xend\_start ignore) (on\_xend\_stop ignore) (cpu\_time 147464.486225) (online\_vcpus 4) (image (linux (kernel ) (superpages 0) (nomigrate 0) (tsc\_mode 0))) (status 2) (state r-----) ) I find it difficult to believe that the hypervisor is only using 74 MB!!! 6143-2477-3592 = 74 MB The TID suggests that I need to make -all memory- available to Dom0 for this calculation to work. I don’t know where the 2477 MB limit is set and I don’t see how I can change the Dom0 settings as I would for a DomU. Any ideas? ## – Kevin Boyle If you find this post helpful, please click on the star below! KBOYLE’s Profile: [http://forums.novell.com/member.php?userid=19359](http://forums.novell.com/member.php?userid=19359) View this thread: [http://forums.novell.com/showthread.php?t=447175](http://forums.novell.com/showthread.php?t=447175) ---
**Author:** ![system](https://us1.discourse-cdn.com/flex022/uploads/suse/original/2X/5/5012ba89e3ffb5220dac47d5ea0ba032e2fe1cb6.png) [@system](https://forums.suse.com/u/system)\ **Post date:** [October 26, 2011, 8:23pm UTC](https://forums.suse.com/t/calculating-memory-used-by-xen-hypervisor/22063/2 "2011-10-26T20:23:23Z")
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