linux-kernel - Re: [RFC Patch 0/2] KVM: SVM: Cgroup support for SVM SEV ASIDs

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Message-ID: <20201124231814.GA258638@google.com>
Date:   Tue, 24 Nov 2020 23:18:14 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     David Rientjes <rientjes@...gle.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas <thomas.lendacky@....com>, pbonzini@...hat.com,
        tj@...nel.org, lizefan@...wei.com, joro@...tes.org, corbet@....net,
        Brijesh <brijesh.singh@....com>, Jon <jon.grimm@....com>,
        Eric <eric.vantassell@....com>, gingell@...gle.com,
        kvm@...r.kernel.org, x86@...nel.org, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC Patch 0/2] KVM: SVM: Cgroup support for SVM SEV ASIDs

On Tue, Nov 24, 2020, Vipin Sharma wrote:
> On Tue, Nov 24, 2020 at 09:27:25PM +0000, Sean Christopherson wrote:
> > Is a root level stat file needed?  Can't the infrastructure do .max - .current
> > on the root cgroup to calculate the number of available ids in the system?
> 
> For an efficient scheduling of workloads in the cloud infrastructure, a
> scheduler needs to know the total capacity supported and the current
> usage of the host to get the overall picture. There are some issues with
> .max -.current approach:
> 
> 1. Cgroup v2 convention is to not put resource control files in the
>    root. This will mean we need to sum (.max -.current) in all of the
>    immediate children of the root.

Ah, that's annoying.  Now that you mention it, I do vaguely recall this behavior.
 
> 2. .max can have any limit unless we add a check to not allow a user to
>    set any value more than the supported one. 

Duh, didn't think that one through.

Thanks!