linux-kernel - Re: [PATCH v6 21/29] KVM: Resolve memslot ID via a hash table instead of via a static array

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Message-ID: <c1dca71f-99d7-93b2-b4fe-d02526fefc81@maciej.szmigiero.name>
Date:   Wed, 1 Dec 2021 16:45:29 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Igor Mammedov <imammedo@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Atish Patra <atish.patra@....com>,
        Ben Gardon <bgardon@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 21/29] KVM: Resolve memslot ID via a hash table instead
 of via a static array

On 01.12.2021 03:54, Sean Christopherson wrote:
> On Tue, Nov 30, 2021, Maciej S. Szmigiero wrote:
>> From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
>>
>> Memslot ID to the corresponding memslot mappings are currently kept as
>> indices in static id_to_index array.
>> The size of this array depends on the maximum allowed memslot count
>> (regardless of the number of memslots actually in use).
>>
>> This has become especially problematic recently, when memslot count cap was
>> removed, so the maximum count is now full 32k memslots - the maximum
>> allowed by the current KVM API.
>>
>> Keeping these IDs in a hash table (instead of an array) avoids this
>> problem.
>>
>> Resolving a memslot ID to the actual memslot (instead of its index) will
>> also enable transitioning away from an array-based implementation of the
>> whole memslots structure in a later commit.
>>
>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
>> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> 
> Nit, your SoB should come last since you were the last person to handle the patch.
> 

Thought that my SoB should come first as coming from the author of this
patch.

Documentation/process/submitting-patches.rst says that:
> Any further SoBs (Signed-off-by:'s) following the author's SoB are from
> people handling and transporting the patch, but were not involved in its
> development. SoB chains should reflect the **real** route a patch took
> as it was propagated to the maintainers and ultimately to Linus, with
> the first SoB entry signalling primary authorship of a single author.

So "further SoBs follow[] the author's SoB" and "the first SoB entry
signal[s] primary authorship".
But at the same time "SoB chains should reflect the **real** route a
patch took" - these rules contradict each other in our case.

Thanks,
Maciej