[Discussion] Serial GC: Expand young generation size

[Kirk Pepperdine]

Hi Albert,

We are working on adding automated heap sizing (AHS) to the serial collector. One of the issues that we’re looking at is how to expand (or contract) heap as needed. One of the challenges in expanding young gen is the location of data in the heap after a full collection. One of the experiments that we’re currently working on is a rearrangement of the heap so that young can be expanded after a full collection without the need to copy all of the surviving data to accommodate an enlargement of young.

Kind regards,
Kirk

> On Jan 8, 2025, at 11:27 AM, Albert Yang <albert.m.yang at oracle.com> wrote:
> 
> Re https://bugs.openjdk.org/browse/JDK-8333386, I think your suggestion, "add the option `-XX:NewSize=65m`", is the way to go.
> 
> As for adding young-gen expansion support to Serial, it probably should have its own enhancement ticket.
> 
> I am currently working on placing from/to spaces before eden inside young-gen as part of Parallel heap-auto-sizing. I believe Serial can use the same layout (from/to/eden, instead of eden/from/to) to facilitate eden/young-gen expansion. My 2c.
> 
> /Albert
> 
> ________________________________________
> From: hotspot-gc-dev <hotspot-gc-dev-retn at openjdk.org> on behalf of Guoxiong Li <lgxbslgx at gmail.com>
> Sent: Wednesday, January 8, 2025 09:30
> To: hotspot-gc-dev at openjdk.org
> Subject: [Discussion] Serial GC: Expand young generation size
> 
> Hi all,
> 
> Currently, the young generation in SerialGC can't be expanded now
> and is always the initial young generation size. It is not a very big problem generally.
> But in some situations, like JDK-8333386 [1], it will crash the VM (unnecessary OutOfMemoryError).
> 
> So I want to implement the feature to expand the young generation size
> (absolutely, not exceeding the max young generation size).
> What do you think about it? Any ideas will be appreciated.
> 
> Best Regards,
> -- Guoxiong
> 
> Related links:
> [1] https://bugs.openjdk.org/browse/JDK-8333386
> [2] https://bugs.openjdk.org/browse/JDK-8335925
>