ZGC and 1G pages?

[Stefan Karlsson]

Hi Thomas,

On 2023-05-08 10:50, Thomas Stüfe wrote:
> Hi,
>
> ZGC, on Linux, seems only compatible with 2M pages. Seeing that ZGC is 
> often used with very large heaps, is support for 1GB pages planned?

There's currently no plan to support 1GB explicit larges pages.

>
> Especially if one disregards uncommitting (-ZUncommit), 1G pages could 
> be a speed boost for customers with gigantic heaps, as well as reduce 
> their number of VMAs.

One hurdle to get 1GB pages to work is that we take the physical backing 
memory of multiple discontiguous 2MB heap regions and combine them into 
a larger contiguous memory region. To implement 1GB large pages support 
we need to figure out how to perform that detaching of physical memory 
from virtual memory if the 2MB regions reside on 1GB large pages.

StefanK

>
> Thanks, Thomas
>
>