RFR: 8312180: (bf) MappedMemoryUtils passes incorrect arguments to msync (aix)

[Brian Burkhalter]

On Mon, 17 Jul 2023 17:21:01 GMT, Tyler Steele <tsteele at openjdk.org> wrote:

> Calls to `msync` on AIX require the length to be a multiple of a specific pagesize which may not be the same as the one returned by `Bits.pageSize()`, as explained in the JBS issue description.
> 
>> EINVAL The addr argument is not a multiple of the page size as **returned by the sysconf subroutine using the _SC_PAGE_SIZE value for the Name parameter**, ...
> [emphasis added by me]
> 
> By adding this as platform dependant code, the correct value of page size is used on AIX. Other Unix platforms should see no change by calling sysconf instead of Bits.pagesize. Windows is unchanged.

src/java.base/share/classes/java/nio/MappedMemoryUtils.java line 172:

> 170:     private static int pageSize() {
> 171:         int ps = pageSize0();
> 172:         if (ps > 0) {

If `sysconf(_SC_PAGESIZE)` returns a value different from `Bits::pageSize` on other Unix platforms, this could cause an unexpected change in behavior.

src/java.base/share/classes/java/nio/MappedMemoryUtils.java line 175:

> 173:             return ps;
> 174:         } else {
> 175:             return Bits.pageSize();

`Bits::pageSize` returns `UnsafeConstants::PAGE_SIZE` which is injected by the VM. Could it be that that value is somehow derived differently on AIX?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14904#discussion_r1266098076
PR Review Comment: https://git.openjdk.org/jdk/pull/14904#discussion_r1266098155