PRT memory usage

[Milan Mimica]

Hello Thomas

pon, 21. kol 2017. u 18:42 Thomas Schatzl <thomas.schatzl at oracle.com>
napisao je:

> > need you to confirm. Given region size of 8M and default G1 settings:
> > * max number of PRT instances is 2^12 for each HR
>
> Where did you get the 2^12 from?
>

A bit simplified calculation of OtherRegionsTable::_max_fine_entries:
_max_fine_entries = G1RSetRegionEntries = G1RSetRegionEntriesBase *
(region_size_log_mb + 1)
where:
G1RSetRegionEntriesBase = 256
region_size_log_mb ... is 3, not 23. Ok, I made a mistake here.

> * PRT size is 64MB
>
> Not completely following, where from do you understand that max prt
> size is 64MB?
>

> 8M region size implies a 2k PRT (bitmap) size (one bit per 512 bytes)
>

Ah yes, my bed. It made several miscalculations also here.

> Do only Young HR get a OtherRegionsTable?
>
> All regions get them. But there are no PRTs from young regions to old
> regions. Humongous continues regions don't have any remembered set.
>

So there is only old-to-young, for each young?

> Where can I find the number of regions per generation? I cannot spot
> > it in GC logs.
>
> -Xlog:gc+heap=info gives you the following kind of output:
>
>
Great. Thanks!

Since e2 is slightly more memory efficient, it might be worth trying to
> bump G1RSetSparseRegionEntries.
>

You don't remember, but we've gone through this some months ago. It did
help indeed. Thanks again.

If you think all what I explained above is gibberish to you, and
> you are still interested, I can try to explain it a bit better :)
>

No, I actually understood everything, and have gone through all this in the
code already.
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