RFR: 8366854: Extend jtreg failure handler with THP info

[Stefan Johansson]

On Thu, 4 Sep 2025 07:03:01 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> I propose that we also dump /proc/meminfo, /proc/vmstat, and /sys/kernel/mm/transparent_hugepage/{enabled, defrag} from the failure handler.
> 
> This information has been helpful when investigating a failure where there was an unexpected lack of transparent huge pages.

Thanks for fixing this @stefank 

This was really helpful when we debugged a THP issue recently, so good to get it into the mainline.

test/failure_handler/src/share/conf/linux.properties line 127:

> 125: memory.proc_vmstat.delimiter=\0
> 126: memory.thp.app=bash
> 127: memory.thp.args=-c\0cat /sys/kernel/mm/transparent_hugepage/{enabled,defrag}

I think we should include `shmem_enabled` and we could use `tail` if we want to see what files have what info. But I don't have a strong feeling about that:

$ cat /sys/kernel/mm/transparent_hugepage/{enabled,defrag,shmem_enabled}
always [madvise] never
always defer defer+madvise [madvise] never
always within_size advise [never] deny force

Versus:

$ tail /sys/kernel/mm/transparent_hugepage/{enabled,defrag,shmem_enabled}
==> /sys/kernel/mm/transparent_hugepage/enabled <==
always [madvise] never

==> /sys/kernel/mm/transparent_hugepage/defrag <==
always defer defer+madvise [madvise] never

==> /sys/kernel/mm/transparent_hugepage/shmem_enabled <==
always within_size advise [never] deny force

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

Marked as reviewed by sjohanss (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27086#pullrequestreview-3183836877
PR Review Comment: https://git.openjdk.org/jdk/pull/27086#discussion_r2321120030