On Wed, Feb 26, 2014 at 01:45:38PM +0100, Paolo Bonzini wrote: > Il 26/02/2014 13:31, Igor Mammedov ha scritto: > >>> The problem is that some backends might not be handled the same way. > >>> For example, not all backends might produce a single void*/size_t pair > >>> for the entire region. Think of a "composite" backend that produces a > >>> large memory region from two smaller ones. > >I'd prefer to keep backends simple, with 1:1 mapping to memory regions. > > I agree. However not all backends may have a mapping to a RAM > memory region. A composite backend could create a container memory > region whose children are other HostMemoryBackend objects. > > >Is there a need in composite one or something similar? > > I've heard of users that want a node backed partially by hugetlbfs > and partially by regular RAM. Not sure why. > > Paolo
To overcommit the non hugetlbfs backed guest RAM (think guest pagecache on that non hugetlbfs backed memory, swappable and KSM-able). The problem is, you have to in someway guarantee the guest allocates 1GB pages out of the hugetlb backed GPA ranges. Some thoughts (honestly, dislike all of them): 1) Boot guest with hugepages, allocate hugepages in guest, later on hotplug 4K backed ranges. HV-unaware reboot might fail, though. 2) Communicate hugepage GPAs to guest. 3) Create holes in non hugepage backed GPA range.
