linux-kernel - Re: On guest free page hinting and OOM

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Date:   Tue, 2 Apr 2019 11:25:10 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com,
        pagupta@...hat.com, wei.w.wang@...el.com,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Rik van Riel <riel@...riel.com>, dodgen@...gle.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: On guest free page hinting and OOM

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.


-- 
MST