RFR: 6980847: (fs) Files.copy needs to be tuned [v5]

[Brian Burkhalter]

On Thu, 16 Jun 2022 23:36:34 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Modify `UnixCopyFile.copyFile()` to set the transfer size to the least common multiple of the source and destination file block sizes if the block sizes are not equal. Modify `WindowsFileCopy.copy()` to set `COPY_FILE_NO_BUFFERING` in the flags passed to `CopyFileEx()` if the size of the transfer is greater than a threshold.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   6980847: Use temporary direct buffer for user-space copy

Benchmark numbers for temporary direct buffers (commit c30a6f0be3f45e30c32fbaf7cbd48ea96ca0e450):

Benchmark      (length)   Mode  Cnt      Score     Error  Units
CopyFile.copy     10000  thrpt   10  31927.639 ± 349.679  ops/s
CopyFile.copy    100000  thrpt   10  12155.232 ± 118.164  ops/s
CopyFile.copy   1000000  thrpt   10   1680.935 ±  36.228  ops/s
CopyFile.copy  10000000  thrpt   10    119.173 ±   1.992  ops/s

These are similar to the measurement of the previous version (commit 0a77bd26e2542f98b42bb65b716738e75f6979bc) but have neither stack nor malloc'ed memory.

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PR: https://git.openjdk.org/jdk/pull/9161