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

Christian Borntraeger
2019-10-23T18:56:38Z

On 22.10.19 15:59, Paolo Bonzini wrote:
> 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
>>
>> Sean Christopherson (15):
>> KVM: Reinstall old memslots if arch preparation fails
>> KVM: Don't free new memslot if allocation of said memslot fails
>> KVM: PPC: Move memslot memory allocation into prepare_memory_region()
>> KVM: x86: Allocate memslot resources during prepare_memory_region()
>> KVM: Drop kvm_arch_create_memslot()
>> KVM: Explicitly free allocated-but-unused dirty bitmap
>> KVM: Refactor error handling for setting memory region
>> KVM: Move setting of memslot into helper routine
>> KVM: Move memslot deletion to helper function
>> KVM: Simplify kvm_free_memslot() and all its descendents
>> KVM: Clean up local variable usage in __kvm_set_memory_region()
>> KVM: Provide common implementation for generic dirty log functions
>> KVM: Ensure validity of memslot with respect to kvm_get_dirty_log()
>> KVM: Terminate memslot walks via used_slots
>> KVM: Dynamically size memslot array based on number of used slots
>>
>> arch/mips/include/asm/kvm_host.h | 2 +-
>> arch/mips/kvm/mips.c | 68 +---
>> arch/powerpc/include/asm/kvm_ppc.h | 14 +-
>> arch/powerpc/kvm/book3s.c | 22 +-
>> arch/powerpc/kvm/book3s_hv.c | 36 +-
>> arch/powerpc/kvm/book3s_pr.c | 20 +-
>> arch/powerpc/kvm/booke.c | 17 +-
>> arch/powerpc/kvm/powerpc.c | 13 +-
>> arch/s390/include/asm/kvm_host.h | 2 +-
>> arch/s390/kvm/kvm-s390.c | 21 +-
>> arch/x86/include/asm/kvm_page_track.h | 3 +-
>> arch/x86/kvm/page_track.c | 15 +-
>> arch/x86/kvm/x86.c | 100 ++---
>> include/linux/kvm_host.h | 48 +--
>> virt/kvm/arm/arm.c | 47 +--
>> virt/kvm/arm/mmu.c | 18 +-
>> virt/kvm/kvm_main.c | 546 ++++++++++++++++----------
>> 17 files changed, 467 insertions(+), 525 deletions(-)
>>
>
> Christian, Marc, Paul, can you help testing patches 1-13?

I see no obvious breakage on s390, but I will do some more testing in the next days.