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

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Message-ID: <2fc05685467a01c2f1c2afeacefb2f68@www.loen.fr>
Date:   Fri, 25 Oct 2019 17:30:20 +0100
From:   Marc Zyngier <maz@...nel.org>
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>,
        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 2019-10-25 00:07, 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.

I've finally found time to test this on a garden variety of arm64 
boxes,
and nothing caught fire. It surely must be doing something right!

FWIW:

Tested-by: Marc Zyngier <maz@...nel.org>

         M.
-- 
Jazz is not dead. It just smells funny...