Re: [Xen-devel] [PATCH Remus v5 2/2] libxc/restore: implement Remus checkpointed restore

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/05/15 10:27, Ian Campbell wrote:
> On Fri, 2015-05-15 at 17:19 +0800, Yang Hongyang wrote:
>> On 05/15/2015 05:09 PM, Ian Campbell wrote:
>>> On Fri, 2015-05-15 at 09:32 +0800, Yang Hongyang wrote:
>>>> On 05/14/2015 09:05 PM, Ian Campbell wrote:
>>>>> On Thu, 2015-05-14 at 18:06 +0800, Yang Hongyang wrote:
>>>>>> With Remus, the restore flow should be:
>>>>>> the first full migration stream -> { periodically restore stream }
>>>>>>
>>>>>> Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
>>>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>>>>>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>>>>>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>>>>>> ---
>>>>>>    tools/libxc/xc_sr_common.h  |  14 ++++++
>>>>>>    tools/libxc/xc_sr_restore.c | 113 
>>>>>> ++++++++++++++++++++++++++++++++++++++++----
>>>>>>    2 files changed, 117 insertions(+), 10 deletions(-)
>>>>>>
>>>>>> diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
>>>>>> index f8121e7..3bf27f1 100644
>>>>>> --- a/tools/libxc/xc_sr_common.h
>>>>>> +++ b/tools/libxc/xc_sr_common.h
>>>>>> @@ -208,6 +208,20 @@ struct xc_sr_context
>>>>>>                /* Plain VM, or checkpoints over time. */
>>>>>>                bool checkpointed;
>>>>>>
>>>>>> +            /* Currently buffering records between a checkpoint */
>>>>>> +            bool buffer_all_records;
>>>>>> +
>>>>>> +/*
>>>>>> + * With Remus, we buffer the records sent by the primary at checkpoint,
>>>>>> + * in case the primary will fail, we can recover from the last
>>>>>> + * checkpoint state.
>>>>>> + * This should be enough because primary only send dirty pages at
>>>>>> + * checkpoint.
>>>>> I'm not sure how it then follows that 1024 buffers is guaranteed to be
>>>>> enough, unless there is something on the sending side arranging it to be
>>>>> so?
>>>> There are only few records at every checkpoint in my test, mostly under 10,
>>>> probably because I don't do much operations in the Guest. I thought This 
>>>> limit
>>>> can be adjusted later by further testing.
>>> For some reason I thought these buffers included the page data, is that
>>> not true? I was expecting the bulk of the records to be dirty page data.
>> The page data is not stored in this buffer, but it's pointer stored in
>> this buffer(rec->data). This buffer is the bulk of the struct xc_sr_record.
> OK, so there are (approximately) as many xc_sr_records as there are
> buffered dirty pages?

Every PAGE_DATA record can have as many pages in it as it wishes,
subject to the (arbitrary) 8MB max record length.

The sending side will typically put 1024 pages in an individual record.

~Andrew

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