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

[Juan Quintela <quintela@redhat.com>]

"Shribman, Aidan" <aidan.shribman@sap.com> wrote:
>> On Wed, May 11, 2011 at 8:58 AM, Shribman, Aidan 
>> <aidan.shribman@sap.com> wrote:
>> > From: Aidan Shribman <aidan.shribman@sap.com>
>> >
>> > [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?

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.