On Fri, Nov 05, 2021, Marc Zyngier wrote: > At least on arm64 and x86, the vcpus array is pretty huge (512 entries), > and is mostly empty in most cases (running 512 vcpu VMs is not that > common). This mean that we end-up with a 4kB block of unused memory > in the middle of the kvm structure. Heh, x86 is now up to 1024 entries. > Instead of wasting away this memory, let's use an xarray instead, > which gives us almost the same flexibility as a normal array, but > with a reduced memory usage with smaller VMs. > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> > --- > @@ -693,7 +694,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i) > > /* Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu. */ > smp_rmb(); > - return kvm->vcpus[i]; > + return xa_load(&kvm->vcpu_array, i); > } It'd be nice for this series to convert kvm_for_each_vcpu() to use xa_for_each() as well. Maybe as a patch on top so that potential explosions from that are isolated from the initiali conversion? Or maybe even use xa_for_each_range() to cap at online_vcpus? That's technically a functional change, but IMO it's easier to reason about iterating over a snapshot of vCPUs as opposed to being able to iterate over vCPUs as their being added. In practice I doubt it matters. #define kvm_for_each_vcpu(idx, vcpup, kvm) \ xa_for_each_range(&kvm->vcpu_array, idx, vcpup, 0, atomic_read(&kvm->online_vcpus))
