linux-kernel - Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays

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Message-ID: <20191023093954.GH2652@e113682-lin.lund.arm.com>
Date:   Wed, 23 Oct 2019 11:39:54 +0200
From:   Christoffer Dall <christoffer.dall@....com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Cornelia Huck <cohuck@...hat.com>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        kvmarm@...ts.cs.columbia.edu, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays

On Mon, Oct 21, 2019 at 05:35:22PM -0700, 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 12/13 and 13/13.  Patches 1-11
> clean up the memslot code, which has gotten quite crusy, 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.
> 
> Testing, especially non-x86 platforms, would be greatly appreciated.  The
> non-x86 changes are for all intents and purposes untested, e.g. I compile
> tested pieces of the code by copying them into x86, but that's it.  In
> theory, the vast majority of the functional changes are arch agnostic, in
> theory...

I've built this for arm/arm64, and I've ran my usual set of tests which
pass fine.  I've also run the selftest framework's tests for the dirty
logging and the migration loop test for arm64, and they pass fine.

You can add my (for arm64):

Tested-by: Christoffer Dall <christoffer.dall@....com>