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Date:   Tue, 10 Aug 2021 14:20:08 -0700
From:   Andi Kleen <>
To:     Dave Hansen <>,
        "Kirill A. Shutemov" <>,
        Borislav Petkov <>,
        Andy Lutomirski <>,
        Sean Christopherson <>,
        Andrew Morton <>,
        Joerg Roedel <>
Cc:     Kuppuswamy Sathyanarayanan 
        David Rientjes <>,
        Vlastimil Babka <>,
        Tom Lendacky <>,
        Thomas Gleixner <>,
        Peter Zijlstra <>,
        Paolo Bonzini <>,
        Ingo Molnar <>,
        Varad Gautam <>,
        Dario Faggioli <>,,,,,
        "Kirill A. Shutemov" <>
Subject: Re: [PATCH 1/5] mm: Add support for unaccepted memory

> These boot blips are not the biggest issue in the world.  But, it is
> fully under the guest's control and I think the guest has some
> responsibility to provide *some* mitigation for it.

It sounds more like an exercise in preliminary optimization at this 
point. If it's a real problem we can still worry about it later.

> 1. Do background acceptance, as opposed to relying 100% on demand-driven
>     acceptance.  Guarantees a limited window in which blips can occur.

Like Kirill wrote this was abandoned because it always allocates all 
memory on the host even if the guest doesn't need it.

> 2. Do acceptance based on user input, like from sysfs.

You can easily do that by running "memhog" at boot. No need for anything 
in the kernel.

BTW I believe this is also configurable at the guest BIOS level.

> 3. Add a command-line argument to accept everything up front, or at
>     least before userspace runs.


> 4. Add some statistic for how much unaccepted memory remains.

Yes that makes sense. We should have statistic counters for all of this.

Also I agree with your suggestion that we should get the slow path out 
of the zone locks/interrupt disable region. That should be easy enough 
and is an obvious improvement.


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