Re: [PATCH v11 4/6] x86/sev: Add support to perform RMP optimizations asynchronously

[Borislav Petkov]

On Tue, Aug 04, 2026 at 09:38:05PM -0500, Kalra, Ashish wrote:
> - Under churn (many SNP guests terminating and respawning), an hourly scan
> is too coarse — freed regions would sit un-optimized for up to an hour. The
> teardown trigger re-optimizes right after each burst of terminations
> (batched by the timeout), so it's more responsive than a periodic scan
> exactly when there's the most optimization work to do.

Yes.

> - When no SNP guests run, a periodic scan achieves nothing: the initial pass
> already optimized all of memory and nothing has changed, so it just re-scans
> physmem for zero benefit.

Well, no. You won't even run that when there are no SNP guests present.

> So the event-driven approach self-scales with real work — it runs as often
> as memory is actually freed and not at all when the system is idle — whereas
> a fixed timer is both too slow under load and pure overhead when idle. The
> mid-life contiguous-1 GB case is then caught precisely by the 1 GB-hugetlb
> page-cleanup hook when that lands, rather than by a coarse sweep.

I wanted to have this in case pages do get freed up from time to time and you
get some sort of a fragmentation. But I'm being told that we don't support
balooning yet, neither memory hotplug and when the pages get freed, they
remain guest-owned. So yes, the points in time where those page become
HV-owned and potentially freed, then we should optimize.

Please hold down that in the commit message so that it is clear for future
readers why we did it this way.

Thx.

-- 
Regards/Gruss,
    Boris.

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