On Fri, 5 Sep 2025 07:02:46 GMT, Stefan Johansson <sjoha...@openjdk.org> wrote:
>> Please review this enhancement to the smaps parser and printer. >> >> **Summary** >> While working on [JDK-8366434](https://bugs.openjdk.org/browse/JDK-8366434) >> one idea for a test to verify if the heap CAN be backed by transparent huge >> pages (THP) was to use PrintMemoryMapAtExit and look at the tags printed for >> JAVAHEAP. >> >> It turns out this worked in most cases but on systems where the THP mode is >> configured as 'always' but there are no huge pages available for use, the >> JAVAHEAP line will not show any indication that it can be backed by huge >> pages. >> >> For this to be possible we need to parse the field THPeligible as well and >> include this information in the printouts. With this change we now parse the >> THPeligible field and tag mapping that are THP eligible with `thpel`. We >> skip this tag for mappings that are tagged with `thpad` (madvised with >> MADV_HUGEPAGE) to avoid too much THP info on one mapping. >> >> **Testing** >> * Mach5 testing with the existing test showed a need to update the regex for >> verifying Metaspace and the fix have been tested manually locally as well as >> in Mach5. > > Stefan Johansson has updated the pull request incrementally with one > additional commit since the last revision: > > Albert review After some offline discussion we've decided to not filter away `thpel` for mappings with the `thpad` tag set, because a mapping can have the `thpad` tag but not bet THPeligible. For example if you would `madvise` a too small region. So showing both tags have a value. Also changing the order of the THP tags to be in order of significance: thp - mapping backed by at least one huge page thpel - OS marked mapping as eligible for huge pages thpad - JVM requested mapping to be backed by huge pages ------------- PR Comment: https://git.openjdk.org/jdk/pull/27098#issuecomment-3257516929
