From: David Hildenbrand <david@redhat.com>
To: "Michael S. Tsirkin" <mst@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 16:45:58 +0100 [thread overview]
Message-ID: <f0ee075d-3e99-efd5-8c82-98d53b9f204f@redhat.com> (raw)
In-Reply-To: <7a3baa90-5963-e6e2-c862-9cd9cc1b5f60@redhat.com>
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.
Oh, and before I forget, different zones might of course also be a problem.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-03-29 15:46 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 [this message]
2019-03-29 16:51 ` Michael S. Tsirkin
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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