ZGC and 1G pages?

[Thomas Stüfe]

Hi Stefan,

On Mon, May 8, 2023 at 11:08 AM Stefan Karlsson <stefan.karlsson at oracle.com>
wrote:

> 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.
>

Thank you for clarifying!

This is probably a naive question, but would increasing the zpage size to
1GB be a valid option?

..Thomas


> StefanK
>
> >
> > Thanks, Thomas
> >
> >
>
>
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