linux-kernel - Re: [PATCH v3 00/15] KVM: Dynamically size memslot arrays

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Date:   Mon, 16 Dec 2019 09:25:24 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.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,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH v3 00/15] KVM: Dynamically size memslot arrays



On 13.12.19 21:01, Sean Christopherson wrote:
> On Tue, Dec 03, 2019 at 02:14:33PM -0800, Sean Christopherson wrote:
>> On Thu, Oct 24, 2019 at 04:07:29PM -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 14/15 and 15/15.  Patches 1-13
>>> clean up the memslot code, which has gotten quite crusty, 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.
>>>
>>> Christoffer, I added your Tested-by to the patches that I was confident
>>> would be fully tested based on the desription of what you tested.  Let me
>>> know if you disagree with any of 'em.
>>>
>>> v3:
>>>   - Fix build errors on PPC and MIPS due to missed params during
>>>     refactoring [kbuild test robot].
>>>   - Rename the helpers for update_memslots() and add comments describing
>>>     the new algorithm and how it interacts with searching [Paolo].
>>>   - Remove the unnecessary and obnoxious warning regarding memslots being
>>>     a flexible array [Paolo].
>>>   - Fix typos in the changelog of patch 09/15 [Christoffer].
>>>   - Collect tags [Christoffer].
>>>
>>> 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
>>
>> Paolo, do you want me to rebase this to the latest kvm/queue?
> 
> Ping.
> 
> Applies cleanly on the current kvm/queue and nothing caught fire in
> testing (though I only re-tested the series as a whole).

Do you have the latest version somewhere on a branch? The version on the
list no longer applies cleanly.