Re: [Qemu-devel] [PATCH] Add warmup phase for live migration of large memory apps

[Yoshiaki Tamura]

2011/5/12 Isaku Yamahata <address@hidden>:
> On Thu, May 12, 2011 at 12:39:22PM +0200, Juan Quintela wrote:
>> "Shribman, Aidan" <address@hidden> wrote:
>> >> On Wed, May 11, 2011 at 8:58 AM, Shribman, Aidan
>> >> <address@hidden> wrote:
>> >> > From: Aidan Shribman <address@hidden>
>> >> >
>> >> > [PATCH] Add warmup phase for live migration of large memory apps
>> >> >
>> >> > By invoking "migrate -w <url>" we initiate a background
>> >> live-migration
>> >> > transferring of dirty pages continuously until invocation
>> >> of "migrate_end"
>> >> > which attempts to complete the live migration operation.
>> >>
>> >> What is the purpose of this patch?  How and when do I use it?
>> >>
>> >
>> > The warmup patch adds none-converging background update of guest
>> > memory during live-migration such that on request of live-migration
>> > completion (via "migrate_end" command) we get much faster
>> > response. This is especially needed when running a payload of large
>> > enterprise applications which have high memory demands.
>>
>> We should integrate this with Kemari (Kemari is doing something like
>> this, just that it has more requirements).  Isaku, do you have any comments?
>
> Yochi and Kei are familiar with Kemari. Not me. Cced to them.

I think it's OK to have this feature by checking max_downtime ==
0.  But I'm wondering that if users type commands like:

migrate_set_downtime 0
migrate <url> # w/o -d

it'll lock the monitor forever in most cases.  So forcing users to
set -d or automatically doing inside in case of max_downtime == 0
seems better to me.  Sorry if I'm missing the point...

Yoshi

>
>
>>
>> BTW, what loads have you tested for this?
>>
>> if I setup an image with 1GB RAM and a DVD iso image, and do in the
>> guest:
>>
>> while true; do find /media/cdrom -type f | xargs md5sum; done
>>
>> Migration never converges with current code (if you use more than 1GB
>> memory, then all the DVD will be cached inside).
>>
>> So, I see this only useful for guests that are almost idle, and on that
>> case, migration speed is not the bigger of your problems, no?
>>
>> Later, Juan.
>>
>
> --
> yamahata
>