Re: [PATCH 1/5] mm: Add support for unaccepted memory

Andi Kleen
2021-08-10T21:20:18Z

> 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