RFR: 8244847: Linux/PPC: runtime/CompressedOops/CompressedClassPointers: smallHeapTest fails [v2]

[Richard Reingruber]

> This is an XS sized patch to get a zerobased compressed class space on
> Linux/PPC64 if a heap up to 2g size is configured and CDS is disabled.
> 
> On Linux 4.1.42 and higher we fail to get a zerobased CCS because just one
> attempt is made to place the CCS right after the heap which will be at 4g
> (ELF_ET_DYN_BASE) but there the java launcher is already mapped.
> 
> This change reuses the search already implemented for AARCH64.
> 
>                   Master without Fix                               Master with Fix
> 
> -Xmx   Narrow klass base     Compressed Class Space    Narrow klass base     Compressed Class Space
> ----------------------------------------------------------------------------------------------------
> 512m   0x00007fff00000000 !  0x00007fff00000000        0x0000000000000000    0x0000000200000000
>   1g   0x00007fff14000000 !  0x00007fff14000000        0x0000000000000000    0x0000000200000000
>   2g   0x00007fff30000000 !  0x00007fff30000000        0x0000000000000000    0x0000000200000000
>   3g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>   4g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>   8g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>  12g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>  16g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>  20g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>  24g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
>  28g   0x0000001702000000    0x0000001702000000        0x0000001702000000    0x0000001702000000
>  32g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000
>  40g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000
>  48g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000

Richard Reingruber has updated the pull request incrementally with one additional commit since the last revision:

  Special case for AIX in largeHeapTest().

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1512/files
  - new: https://git.openjdk.java.net/jdk/pull/1512/files/d8e6d143..c78783cc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1512&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1512&range=00-01

  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1512.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1512/head:pull/1512

PR: https://git.openjdk.java.net/jdk/pull/1512