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

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Date:   Mon, 1 Apr 2019 16:54:49 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 01.04.19 16:47, Michael S. Tsirkin wrote:
> On Mon, Apr 01, 2019 at 04:11:42PM +0200, David Hildenbrand wrote:
>>> The interesting thing is most probably: Will the hinting size usually be
>>> reasonable small? At least I guess a guest with 4TB of RAM will not
>>> suddenly get a hinting size of hundreds of GB. Most probably also only
>>> something in the range of 1GB. But this is an interesting question to
>>> look into.
>>>
>>> Also, if the admin does not care about performance implications when
>>> already close to hinting, no need to add the additional 1Gb to the ram size.
>>
>> "close to OOM" is what I meant.
> 
> Problem is, host admin is the one adding memory. Guest admin is
> the one that knows about performance.

If we think about guest admins only caring about performance, then a
guest admin owill unloads virtio-balloon module to

a) get all the memory available (inflated memory returned to the guest)
b) not use hinting :)

But I get your idea. One side wants hinting, other side has to agree.

-- 

Thanks,

David / dhildenb