JVM Pretouch

[Anton Kozlov]

Hi Martin,

On 11/12/24 1:50 PM, Martin Welgemoed wrote:
> I've been experimenting with CRaC in the Azul image and the benchmarks
> have been truly impressive, thanks for this excellent project!

Thank you!

> First after the restore the effects of "AlwaysPreTouch" have been
> undone.

To keep restore time low, we mmap image pages, o first access will require load
the content first. You can try this before executing restore command:

export CRAC_CRIU_OPTS=--no-mmap-page-image

Now the decision is done by integration with CRIU.It i should make images pages
available right away.

> Secondly, java options such as Xmx are read and processed only once at
> process startup.

Correct, unfortunately. The HotSpot design does not assume the heap size can be
arbitrarily changed. But, it is possible to limit heap growth before
checkpoint, and remove the limit after the restore. We have a very promising
implementation that I hope we'll publish soon.

Thanks,
Anton