Re: [PATCH v4 00/19] KVM: Dynamically size memslot arrays

[Christian Borntraeger]

On 17.12.19 21:40, 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 17/19 and 18/19.
> 
> Patches 2-16 clean up the memslot code, which has gotten quite crusty,
> 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.
> 
> The only functional change in v4 is the addition of an x86-specific bug
> fix in x86's handling of KVM_MR_MOVE.  The bug fix is not directly related
> to dynamically allocating memslots, but it has subtle and hidden conflicts
> with the cleanup patches, and the fix is higher priority than anything
> else in the series, i.e. should be merged first.
> 
> On non-x86 architectures, v3 and v4 should be functionally equivalent,
> the only non-x86 change in v4 is the dropping of a "const" in
> kvm_arch_commit_memory_region().

I gave this series a quick spin and it still seems to work on s390 (minus the selftest).