Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays

Paolo Bonzini
2019-10-22T14:04:54Z

On 22/10/19 02:35, Sean Christopherson wrote:
> The end goal of this series is to dynamically size the memslot array so
> that KVM allocates memory based on the number of memslots in use, as
> opposed to unconditionally allocating memory for the maximum number of
> memslots. On x86, each memslot consumes 88 bytes, and so with 2 address
> spaces of 512 memslots, each VM consumes ~90k bytes for the memslots.
> E.g. given a VM that uses a total of 30 memslots, dynamic sizing reduces
> the memory footprint from 90k to ~2.6k bytes.
>
> The changes required to support dynamic sizing are relatively small,
> e.g. are essentially contained in patches 12/13 and 13/13. Patches 1-11
> clean up the memslot code, which has gotten quite crusy, especially
> __kvm_set_memory_region(). The clean up is likely not strictly necessary
> to switch to dynamic sizing, but I didn't have a remotely reasonable
> level of confidence in the correctness of the dynamic sizing without first
> doing the clean up.
>
> Testing, especially non-x86 platforms, would be greatly appreciated. The
> non-x86 changes are for all intents and purposes untested, e.g. I compile
> tested pieces of the code by copying them into x86, but that's it. In
> theory, the vast majority of the functional changes are arch agnostic, in
> theory...
>
> v2:
> - Split "Drop kvm_arch_create_memslot()" into three patches to move
> minor functional changes to standalone patches [Janosch].
> - Rebase to latest kvm/queue (f0574a1cea5b, "KVM: x86: fix ...")
> - Collect an Acked-by and a Reviewed-by

I only have some cosmetic changes on patches 14-15. Let's wait for
testing results.

Paolo