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

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Message-ID: <129444cc-5211-5b60-15fc-0f0fe998f023@redhat.com>
Date:   Tue, 22 Oct 2019 16:04:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Marc Zyngier <maz@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/15] KVM: Dynamically size memslot arrays

On 22/10/19 02:35, 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...
> 
> v2:
>   - Split "Drop kvm_arch_create_memslot()" into three patches to move
>     minor functional changes to standalone patches [Janosch].
>   - Rebase to latest kvm/queue (f0574a1cea5b, "KVM: x86: fix ...")
>   - Collect an Acked-by and a Reviewed-by

I only have some cosmetic changes on patches 14-15.  Let's wait for
testing results.

Paolo