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

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Message-ID: <20190401104328-mutt-send-email-mst@kernel.org>
Date:   Mon, 1 Apr 2019 10:45:21 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        pbonzini@...hat.com, lcapitulino@...hat.com, pagupta@...hat.com,
        wei.w.wang@...el.com, yang.zhang.wz@...il.com, riel@...riel.com,
        dodgen@...gle.com, konrad.wilk@...cle.com, dhildenb@...hat.com,
        aarcange@...hat.com, alexander.duyck@...il.com
Subject: Re: On guest free page hinting and OOM

On Mon, Apr 01, 2019 at 04:09:32PM +0200, David Hildenbrand wrote:
> > 
> > When you say yield, I would guess that would involve config space access
> > to the balloon to flush out outstanding hints?
> 
> I rather meant yield your CPU to the hypervisor, so it can process
> hinting requests faster (like waiting for a spinlock). This is the
> simple case. More involved approaches might somehow indicate to the
> hypervisor to not process queued requests but simply return them to the
> guest so the guest can add the isolated pages to the buddy. If this is
> "config space access to the balloon to flush out outstanding hints" then
> yes, something like that might be a good idea if it doesn't harm
> performance.

The problem would be in testing this unfortunately. Same as any
OOM hack, it is difficult to test well.

> -- 
> 
> Thanks,
> 
> David / dhildenb