linux-kernel - Re: [PATCH 1/2] KVM: Account memory allocations for 'struct kvm

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Date:   Wed, 31 Mar 2021 11:02:12 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] KVM: Account memory allocations for 'struct kvm_vcpu'

On Wed, 31 Mar 2021 at 10:32, Sean Christopherson <seanjc@...gle.com> wrote:
>
> Use GFP_KERNEL_ACCOUNT for the vCPU allocations, the vCPUs are very much
> tied to a single task/VM.  For x86, the allocations were accounted up
> until the allocation code was moved to common KVM.  For all other
> architectures, vCPU allocations were never previously accounted, but only
> because most architectures lack accounting in general (for KVM).
>
> Fixes: e529ef66e6b5 ("KVM: Move vcpu alloc and init invocation to common code")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  virt/kvm/kvm_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 383df23514b9..3884e9f30251 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3182,7 +3182,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
>         if (r)
>                 goto vcpu_decrement;
>
> -       vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
> +       vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL_ACCOUNT);

kvm_vcpu_cache is created with SLAB_ACCOUNT flag in kvm_init(), this
flag will guarantee further slab alloc will be charged to memcg.
Please refer to memcg_slab_pre_alloc_hook(). So the patch is
unnecessary.

    Wanpeng