Re: On guest free page hinting and OOM

[Michael S. Tsirkin]

On Tue, Apr 02, 2019 at 08:04:00AM -0700, Alexander Duyck wrote:
> Basically what we would be doing is providing a means for
> incrementally transitioning the buddy memory into the idle/offline
> state to reduce guest memory overhead. It would require one function
> that would walk the free page lists and pluck out pages that don't
> have the "Offline" page type set,

I think we will need an interface that gets
an offline page and returns the next online free page.

If we restart the list walk each time we can't guarantee progress.

> a one-line change to the logic for
> allocating a page as we would need to clear that extra bit of state,
> and optionally some bits for how to handle the merge of two "Offline"
> pages in the buddy allocator (required for lower order support). It
> solves most of the guest side issues with the free page hinting in
> that trying to do it via the arch_free_page path is problematic at
> best since it was designed for a synchronous setup, not an
> asynchronous one.


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MST