RFR(S): 8209162: Page size selection does not always select optimal page size

[Stefan Johansson]

Hi Bernd,

Not sure this is exactly what your after, but we have the log-tag 
pagesize. For Parallel you get this:
java -Xlog:pagesize -XX:+UseParallelGC -version
[0.002s][info][pagesize] CodeHeap 'non-nmethods':  min=2496K max=7428K 
base=0x00007f6ae8ceb000 page_size=4K size=7428K
[0.002s][info][pagesize] CodeHeap 'profiled nmethods':  min=2496K 
max=119164K base=0x00007f6ae942c000 page_size=4K size=119164K
[0.002s][info][pagesize] CodeHeap 'non-profiled nmethods':  min=2496K 
max=119168K base=0x00007f6af088b000 page_size=4K size=119168K
[0.003s][info][pagesize] Heap:  min=8M max=8028M base=0x000000060a400000 
page_size=512K size=8028M
[0.003s][info][pagesize] Card Table:  min=16441345B max=16441345B 
base=0x00007f6ae7d3c000 page_size=4K size=16060K
[0.004s][info][pagesize] Mark Bitmap:  min=256896K max=256896K 
base=0x00007f6ad825c000 page_size=4K size=256896K
[0.004s][info][pagesize] Parallel Compact Data:  min=642240B max=642240B 
base=0x00007f6b043b2000 page_size=4K size=628K
[0.004s][info][pagesize] Parallel Compact Data:  min=16056K max=16056K 
base=0x00007f6ad72ae000 page_size=4K size=16056K
java version "15-internal" 2020-09-15
Java(TM) SE Runtime Environment (build 
15-internal+0-2020-04-21-1230537.sjohanss...)
Java HotSpot(TM) 64-Bit Server VM (build 
15-internal+0-2020-04-21-1230537.sjohanss..., mixed mode, sharing)

And if you run it with larger page enabled:
java -Xlog:pagesize -XX:+UseParallelGC -XX:+UseLargePages -version
[0.004s][info][pagesize] CodeHeap 'non-nmethods':  min=2496K max=8M 
base=0x00007f1d00c00000 page_size=4K size=8M
[0.004s][info][pagesize] CodeHeap 'profiled nmethods':  min=2496K 
max=116M base=0x00007f1d01400000 page_size=4K size=116M
[0.004s][info][pagesize] CodeHeap 'non-profiled nmethods':  min=2496K 
max=116M base=0x00007f1d08800000 page_size=4K size=116M
[0.005s][info][pagesize] Heap:  min=8M max=8028M base=0x000000060a400000 
page_size=2M size=8028M
[0.005s][info][pagesize] Card Table:  min=16441345B max=16441345B 
base=0x00007f1d1cba6000 page_size=4K size=16060K
[0.007s][info][pagesize] Mark Bitmap:  min=256896K max=256896K 
base=0x00007f1cf1120000 page_size=4K size=256896K
[0.007s][info][pagesize] Parallel Compact Data:  min=642240B max=642240B 
base=0x00007f1d1c094000 page_size=4K size=628K
[0.007s][info][pagesize] Parallel Compact Data:  min=16056K max=16056K 
base=0x00007f1cf0172000 page_size=4K size=16056K
java version "15-internal" 2020-09-15
Java(TM) SE Runtime Environment (build 
15-internal+0-2020-04-21-1230537.sjohanss...)
Java HotSpot(TM) 64-Bit Server VM (build 
15-internal+0-2020-04-21-1230537.sjohanss..., mixed mode, sharing)

Looks like we have a bug here, when not running with large pages the 
reported heap size for the heap is 512k which is not the page size, but 
the generation alignment.

Hope this helps,
Stefan

On 2020-04-21 20:11, Bernd Eckenfels wrote:
> Related question is there a good way to list in a production JVM what page sizes it has discovered on a specific platform? And has somebody a list of all (supported) platforms (and which page sizes depend on what additional condition).
> 
> I wonder if the divisor of 8 (instead of 4) makes any positive change. For that the typical page sizes would be interesting. This 8 is used in quite a few places, maybe a "regionsize_alignedforgrowth()" would be a way to centralize this?
> 
> Gruss
> Bernd
> --
> http://bernd.eckenfels.net
> ________________________________
> Von: hotspot-gc-dev <hotspot-gc-dev-bounces at openjdk.java.net> im Auftrag von Ivan Walulya <ivan.walulya at oracle.com>
> Gesendet: Dienstag, April 21, 2020 7:51 PM
> An: Thomas Schatzl
> Cc: hotspot-gc-dev
> Betreff: Re: RFR(S): 8209162: Page size selection does not always select optimal page size
> 
> Please find new webrev
> 
> https://cr.openjdk.java.net/~iwalulya/8209162/02/
> 
> //Ivan
> 
>> On 21 Apr 2020, at 17:11, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
>>
>> Hi,
>>
>> On 21.04.20 14:59, Stefan Johansson wrote:
>>> On 2020-04-21 14:44, Thomas Schatzl wrote:
>>>> Hi,
>>>>
>>>> On 21.04.20 14:28, Stefan Johansson wrote:
>>>>>
>>>>>
>>>>> On 2020-04-21 13:22, Thomas Schatzl wrote:
>>>>>> Hi,
>> [...]
>>>>
>>>> Then again, this is parallel gc we are talking about which you likely want to run with -Xms==-Xmx.
>>>>
>>>> The "4" and "8" constants in the code are "random" numbers.
>>> Yeah, the scenarios where the 8 help feels very limited and constructed. I would argue that a 1GB granularity would be a bit much even if the heap is 10g.
>>> In cases where 1g pages are configured I would imagine that the heap sizes used are a lot bigger than this. Kind of like for 2mb page, if it works sub-optimal for 10mb heaps, I'm fine with that.
>>> So are you ok skipping the 8 and just going for not as random 4?
>>
>> That's fine with me. We can change it again.
>>
>> Thomas
>