[libvirt] 1GB huge pages and incompatible VM memory size

[Jim Fehlig]

Hi All,

Matt encountered the following issue when using 1GB huge pages with libvirt

> This problem turned out to be entirely my fault because I didn't round
> the VM's memory size to a 1G multiple, and the kernel tried to split
> the VMA at the end of the region, triggering this code in the kernel
> do_mbind() path,
>
>   static int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
>                 unsigned long addr, int new_below)
>   {
>           struct vm_area_struct *new;
>           int err;
>
>           if (is_vm_hugetlb_page(vma) && (addr &
>                                           ~(huge_page_mask(hstate_vma(vma)))))
>                   return -EINVAL;
>
> I have no idea how a less fortunate developer without access to MM
> experts would have figured this out. It's a shame virsh didn't error
> out when I initially setup 1G hugepages with an incompatible VM memory
> size.

What do folks think about improving libvirt to warn or error when using a VM 
memory size that is not compatible with the host hugepage configuration?

Regards,
Jim