linux-kernel - Re: [PATCH] KVM: arm: memcg awareness

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Message-ID: <e5fce698-9e21-5c71-c99b-a9af3f213e8f@redhat.com>
Date:   Wed, 17 Mar 2021 11:40:23 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Marc Zyngier <maz@...nel.org>, Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>
Subject: Re: [PATCH] KVM: arm: memcg awareness

On 17/03/21 10:10, Marc Zyngier wrote:
>> @@ -366,7 +366,7 @@ static int hyp_map_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
>>   	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
>>   		return -EINVAL;
>>   
>> -	childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL);
>> +	childp = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
> No, this is wrong.
> 
> You cannot account the hypervisor page tables to the guest because we
> don't ever unmap them, and that we can't distinguish two data
> structures from two different VMs occupying the same page.

If you never unmap them, there should at least be a shrinker to get rid 
of unused pages in the event of memory pressure.

Paolo