selftests/mm: add memory-pressure threads to the khugepaged race harness

The harness races collapse against faults, pins, fork, mremap and
MADV_DONTNEED, but nothing in it runs reclaim or compaction against the
collapse.

Add two more threads, and run every mode and occupancy limit both with and
without them:

 - pageout: cycles MADV_PAGEOUT over a region of its own, faults it back
   in and checks the content each round, since a page's pattern must
   survive the trip through swap.  Left out when the host has no swap,
   because then there is no anon reclaim to drive.

 - compactor: writes /proc/sys/vm/compact_memory in a loop.  Compaction
   isolates and migrates folios, so it competes with a collapse for the
   pages it is gathering, with refcount elevations and migration entries
   of its own.

Each result says whether it ran under pressure:

  ok 2 stepped/strict/pressure: 5s, 88 steps, no corruption

A full run is now twelve combinations; -m picks one mode, -d shortens
each run.

Link: https://lore.kernel.org/20260919002451.496763-19-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Assisted-by: LLM
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: "David Hildenbrand (arm)" <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: kernel-team@meta.com
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nico Pache (Red Hat) <nico.pache@linux.dev>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>

0 files changed, 0 insertions, 0 deletions