Allow edit of initial memory size

[mbosma]

Hi Devs,

Using memory hotplug according to the proxmox wiki I succesfully increased and decreased the memory size of a Debian/Ubuntu guest.

However when booting a virtual machine with memory hot-plug enabled and more than 21GB memory the guest OS can kernel panic with the following error:

Kernel panic - not syncing: System is deadlocked on memory

After doing some digging it appears that coldplug of a high amount of memory dimms (70 in my case with 64gb) the 1Gb of initial memory is depleted.
More on this is found on in this thread: https://bugzilla.redhat.com/show_bug.cgi?id=1866360

I used qm showcmd and edited the configuration to start the vm with 4GB initial memory using 2 2048M dimms instead of 2 512M dimms, this allowed the vm to start without issues.

Spoiler: Original

-cpu kvm64,enforce,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep -m 'size=1024,slots=255,maxmem=524288M' -object 'memory-backend-ram,id=ram-node0,size=512M' -numa 'node,nodeid=0,cpus=0-15,memdev=ram-node0' -object 'memory-backend-ram,id=ram-node1,size=512M' -numa 'node,nodeid=1,cpus=16-31,memdev=ram-node1' -object 'memory-backend-ram,id=mem-dimm0,size=512M' -device 'pc-dimm,id=dimm0,memdev=mem-dimm0,node=0' -object 'memory-backend-ram,id=mem-dimm1,size=512M' -device 'pc-dimm,id=dimm1,memdev=mem-dimm1,node=1' -object 'memory-backend-ram,id=mem-dimm2,size=512M' -device 'pc-dimm,id=dimm2,memdev=mem-dimm2,node=0' -object 'memory-backend-ram,id=mem-dimm3,size=512M' -device 'pc-dimm,id=dimm3,memdev=mem-dimm3,node=1'
*TRUNCATED FOR CHARACTER LIMIT*
-object 'memory-backend-ram,id=mem-dimm68,size=2048M' -device 'pc-dimm,id=dimm68,memdev=mem-dimm68,node=0' -object 'memory-backend-ram,id=mem-dimm69,size=2048M' -device 'pc-dimm,id=dimm69,memdev=mem-dimm69,node=1' -object 'memory-backend-ram,id=mem-dimm70,size=2048M' -device 'pc-dimm,id=dimm70,memdev=mem-dimm70,node=0' -object 'memory-backend-ram,id=mem-dimm71,size=2048M' -device 'pc-dimm,id=dimm71,memdev=mem-dimm71,node=1'
*TRUNCATED FOR CHARACTER LIMIT*

Spoiler: 4gb edit

-cpu kvm64,enforce,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep -m 'size=4096,slots=255,maxmem=524288M' -object 'memory-backend-ram,id=ram-node0,size=2048M' -numa 'node,nodeid=0,cpus=0-15,memdev=ram-node0' -object 'memory-backend-ram,id=ram-node1,size=2048M' -numa 'node,nodeid=1,cpus=16-31,memdev=ram-node1' -object 'memory-backend-ram,id=mem-dimm0,size=512M' -device 'pc-dimm,id=dimm0,memdev=mem-dimm0,node=0' -object 'memory-backend-ram,id=mem-dimm1,size=512M' -device 'pc-dimm,id=dimm1,memdev=mem-dimm1,node=1' -object 'memory-backend-ram,id=mem-dimm2,size=512M' -device 'pc-dimm,id=dimm2,memdev=mem-dimm2,node=0' -object 'memory-backend-ram,id=mem-dimm3,size=512M' -device 'pc-dimm,id=dimm3,memdev=mem-dimm3,node=1'
*TRUNCATED FOR CHARACTER LIMIT*
-object 'memory-backend-ram,id=mem-dimm68,size=2048M' -device 'pc-dimm,id=dimm68,memdev=mem-dimm68,node=0' -object 'memory-backend-ram,id=mem-dimm69,size=2048M' -device 'pc-dimm,id=dimm69,memdev=mem-dimm69,node=1' -object 'memory-backend-ram,id=mem-dimm70,size=512M' -device 'pc-dimm,id=dimm70,memdev=mem-dimm70,node=0' -object 'memory-backend-ram,id=mem-dimm71,size=512M' -device 'pc-dimm,id=dimm71,memdev=mem-dimm71,node=1'
*TRUNCATED FOR CHARACTER LIMIT*

In summary, I edited 'size=1024,slots=255,maxmem=524288M' to 'size=4096,slots=255,maxmem=524288M', made the first two dimms 2048M each and the last two to 512M to compensate for that.

Would it be possible to add a variable in memory settings to pass this changed initial memory value to the VM?

I saw some more threads on the forum with describing this same issue so it seems I'm not alone.
Here are a few instances I found:
https://forum.proxmox.com/threads/problem-with-hotplug-and-64gb-ram.73621/post-627640
https://forum.proxmox.com/threads/t...2048-for-hotplugging-still.127632/post-558002
https://forum.proxmox.com/threads/memory-hotplug-system-is-deadlocked-on-memory.115403/post-499639

Shall I open a feature request or does a similar one already exist?

Kind regards

 

[dakralex]

Just for anyone stumbling on this post, the bug report associated with the problem can be seen at [1].

[1] https://bugzilla.proxmox.com/show_bug.cgi?id=5585