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Subject: Re: [PATCH 1/5] mm: Add support for unaccepted memory
To:     Dave Hansen <dave.hansen@intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
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        <sathyanarayanan.kuppuswamy@linux.intel.com>,
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        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
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        Varad Gautam <varad.gautam@suse.com>,
        Dario Faggioli <dfaggioli@suse.com>, x86@kernel.org,
        linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <3caf5e73-c104-0057-680c-7851476e67ac@linux.intel.com>
Date:   Tue, 10 Aug 2021 14:20:08 -0700
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> 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.

Same.


> 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.

-Andi