[Query] Deadlock condition due to virtqueue_add buffer allocation

[Query] Deadlock condition due to virtqueue_add buffer allocation

[Nitesh Narayan Lal]

Hi,

I am working on the guest page hinting support with Rik.
As per my implementation when pages are freed, they are added to a
cpu-local list. Once that list fills up, the pages need to be passed to
the hypervisor. I am currently using a seqlock to ensure page allocation
does not allocate pages while they are being freed by the hypervisor.
This list is passed to the hypervisor using virtio_balloon
infrastructure. As per the current flow virtqueue_add() requires a
memory allocation, which leads to a deadlock condition.

What should be the right way to get around this?

Looking forward for the suggestions.

-- 

Regards
Nitesh

Re: [Query] Deadlock condition due to virtqueue_add buffer allocation

[Yang Zhang]

On 2017/7/29 4:34, Nitesh Narayan Lal wrote:
> Hi,
>
> I am working on the guest page hinting support with Rik.
> As per my implementation when pages are freed, they are added to a
> cpu-local list. Once that list fills up, the pages need to be passed to
> the hypervisor. I am currently using a seqlock to ensure page allocation
> does not allocate pages while they are being freed by the hypervisor.
> This list is passed to the hypervisor using virtio_balloon
> infrastructure. As per the current flow virtqueue_add() requires a
> memory allocation, which leads to a deadlock condition.
>
> What should be the right way to get around this?
>
> Looking forward for the suggestions.
>

Hi Nitesh,

I am interesting on the idea. Could you give more details of the 
background? What page hinting can help and what's the expected usage model?

-- 
Yang
Alibaba Cloud Computing

Re: [Query] Deadlock condition due to virtqueue_add buffer allocation

[Nitesh Narayan Lal]

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On 07/31/2017 11:12 PM, Yang Zhang wrote:
> On 2017/7/29 4:34, Nitesh Narayan Lal wrote:
>> Hi,
>>
>> I am working on the guest page hinting support with Rik.
>> As per my implementation when pages are freed, they are added to a
>> cpu-local list. Once that list fills up, the pages need to be passed to
>> the hypervisor. I am currently using a seqlock to ensure page allocation
>> does not allocate pages while they are being freed by the hypervisor.
>> This list is passed to the hypervisor using virtio_balloon
>> infrastructure. As per the current flow virtqueue_add() requires a
>> memory allocation, which leads to a deadlock condition.
>>
>> What should be the right way to get around this?
>>
>> Looking forward for the suggestions.
>>
>
> Hi Nitesh,
>
> I am interesting on the idea. Could you give more details of the
> background? What page hinting can help and what's the expected usage
> model?
>
Hi Yang,

Basically page hinting support will help in handing of free memory
between the guest and the host rapidly and transparently. It will also
enable the guest to reuse the memory again with the use of MADV_FREE on
the host side.
I will be sharing the first patch-set soon, please feel free to make any
suggestion which you feel are required.

-- 
Regards
Nitesh


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