RFR: JDK-8310110: ShenandoahGC: Trace page sizes

[Aleksey Shipilev]

On Thu, 15 Jun 2023 07:37:11 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> `-Xlog:pagesize` now produced this printout
> 
> 
> [0.006s][info][pagesize] Heap: req_size=5G base=0x00000006c0000000 page_size=1G alignment=1G size=5G
> [0.006s][info][pagesize] Mark Bitmap: req_size=160M base=0x00007fc4c0000000 page_size=1G alignment=1G size=1G
> [0.011s][info][pagesize] Aux Bitmap: req_size=160M base=0x00007fc4c0000000 page_size=1G alignment=1G size=1G
> [0.011s][info][pagesize] Region Storage: req_size=320K base=0x00007fc3c0000000 page_size=1G alignment=1G size=1G
> [0.011s][info][pagesize] Collection Set: req_size=16K base=0x0000000000010000 page_size=4K alignment=4K size=16K
> 
> 
> Note that this printout is from a machine with 1G pages and -XX:+UseLargePages; it nicely demonstrates how much memory we waste in that case on support structures; https://bugs.openjdk.org/browse/JDK-8310111 tracks that.
> 
> Also note that I reuse `os::trace_page_sizes_for_requested_size` here, which I think can be improved and made clearer (alignment is actually requested pagesize). This is tracked separately in https://github.com/openjdk/jdk/pull/14484 .

Oh, also, we try to keep the synopsis format like this: "8310110: Shenandoah: Trace page sizes"

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PR Comment: https://git.openjdk.org/jdk/pull/14486#issuecomment-1594418829