From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, pbonzini@redhat.com, lcapitulino@redhat.com,
pagupta@redhat.com, wei.w.wang@intel.com,
yang.zhang.wz@gmail.com, riel@surriel.com, dodgen@google.com,
konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com,
alexander.duyck@gmail.com
Subject: Re: On guest free page hinting and OOM
Date: Fri, 29 Mar 2019 12:51:26 -0400 [thread overview]
Message-ID: <20190329125034-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <f0ee075d-3e99-efd5-8c82-98d53b9f204f@redhat.com>
On Fri, Mar 29, 2019 at 04:45:58PM +0100, David Hildenbrand wrote:
> On 29.03.19 16:37, David Hildenbrand wrote:
> > On 29.03.19 16:08, Michael S. Tsirkin wrote:
> >> On Fri, Mar 29, 2019 at 03:24:24PM +0100, David Hildenbrand wrote:
> >>>
> >>> We had a very simple idea in mind: As long as a hinting request is
> >>> pending, don't actually trigger any OOM activity, but wait for it to be
> >>> processed. Can be done using simple atomic variable.
> >>>
> >>> This is a scenario that will only pop up when already pretty low on
> >>> memory. And the main difference to ballooning is that we *know* we will
> >>> get more memory soon.
> >>
> >> No we don't. If we keep polling we are quite possibly keeping the CPU
> >> busy so delaying the hint request processing. Again the issue it's a
> >
> > You can always yield. But that's a different topic.
> >
> >> tradeoff. One performance for the other. Very hard to know which path do
> >> you hit in advance, and in the real world no one has the time to profile
> >> and tune things. By comparison trading memory for performance is well
> >> understood.
> >>
> >>
> >>> "appended to guest memory", "global list of memory", malicious guests
> >>> always using that memory like what about NUMA?
> >>
> >> This can be up to the guest. A good approach would be to take
> >> a chunk out of each node and add to the hints buffer.
> >
> > This might lead to you not using the buffer efficiently. But also,
> > different topic.
> >
> >>
> >>> What about different page
> >>> granularity?
> >>
> >> Seems like an orthogonal issue to me.
> >
> > It is similar, yes. But if you support multiple granularities (e.g.
> > MAX_ORDER - 1, MAX_ORDER - 2 ...) you might have to implement some sort
> > of buddy for the buffer. This is different than just a list for each node.
Right but we don't plan to do it yet.
> Oh, and before I forget, different zones might of course also be a problem.
I would just split the hint buffer evenly between zones.
>
> --
>
> Thanks,
>
> David / dhildenb
next prev parent reply other threads:[~2019-03-29 16:51 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-29 13:26 On guest free page hinting and OOM Michael S. Tsirkin
2019-03-29 14:24 ` David Hildenbrand
2019-03-29 15:08 ` Michael S. Tsirkin
2019-03-29 15:37 ` David Hildenbrand
2019-03-29 15:45 ` David Hildenbrand
2019-03-29 16:51 ` Michael S. Tsirkin [this message]
2019-04-01 8:17 ` David Hildenbrand
2019-04-01 13:24 ` Michael S. Tsirkin
2019-04-01 14:09 ` David Hildenbrand
2019-04-01 14:11 ` David Hildenbrand
2019-04-01 14:47 ` Michael S. Tsirkin
2019-04-01 14:54 ` David Hildenbrand
2019-04-01 20:56 ` Alexander Duyck
2019-04-02 7:42 ` David Hildenbrand
2019-04-02 15:04 ` Alexander Duyck
2019-04-02 15:25 ` Michael S. Tsirkin
2019-04-02 15:57 ` David Hildenbrand
2019-04-02 16:18 ` Alexander Duyck
2019-04-02 17:08 ` David Hildenbrand
2019-04-02 17:45 ` Alexander Duyck
2019-04-02 17:53 ` Michael S. Tsirkin
2019-04-02 20:32 ` Alexander Duyck
2019-04-02 18:21 ` David Hildenbrand
2019-04-02 19:49 ` Michael S. Tsirkin
2019-04-02 20:32 ` David Hildenbrand
2019-04-02 15:55 ` David Hildenbrand
2019-04-02 17:30 ` Alexander Duyck
2019-04-02 18:53 ` David Hildenbrand
2019-04-02 23:43 ` Alexander Duyck
2019-04-03 19:43 ` David Hildenbrand
2019-04-04 13:28 ` Michael S. Tsirkin
2019-04-02 16:19 ` David Hildenbrand
2019-04-01 14:45 ` Michael S. Tsirkin
2019-03-29 16:09 ` Michael S. Tsirkin
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