RFR(XXS) 8190729: Adjustment to anonymous metadata space chunk allocation algorithm

[Thomas Stüfe]

Hi Zhengyu,

looks good.

(I wonder whether if you just could have given the SpaceManager a back
pointer to its enclosing Metaspace instead of handing down _space_type and
mdType, but then, those are cleanups we can do later.)

In SpaceManager, could you please make _space_type - and _mdtype too -
const?

Why do you do this only for non-class metaspace?

Could please you embellish the comment in calc_chunk_size() a bit?

Would it be possible to have a regression test for this one, maybe as part
of the NMT tests? So that if we change the allocator logic in the future,
we can be sure not to reintroduce that bug. To me, it would be okay to do
this in a follow up item, if you are concerned about the jdk10 code freeze.

Thank you,

Kind Regards, Thomas


On Mon, Nov 27, 2017 at 6:09 PM, Zhengyu Gu <zgu at redhat.com> wrote:

> Hi,
>
> To follow up recent discussion of anonymous metadata space memory usage, I
> would like submit this simple fix for review.
>
> By continuing allocating anonymous metadata space from SpecializeChunk
> pool, up to 4 chunks, it reduces the waste from 60+% to about 30%.
>
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8190729
> Webrev: http://cr.openjdk.java.net/~zgu/8190729/webrev.00/
>
> Test:
>
>   hotspot_tier1_runtime on Linux x64 (fastdebug and release)
>
>
> Thanks,
>
> -Zhengyu
>