selftests/mm: make the swap cases' swapout reliable

collapse_swapin_single_pte() and collapse_max_ptes_swap() swap a range out
and then require smaps to report exactly the count they asked for.  Two
things keep that count from arriving.

MADV_PAGEOUT is best effort, so the count often turns up a moment late.

And wait_for_scan() leaves the range eligible for collapsing, so
khugepaged is still working on it.  Collapsing reads the swapped-out pages
back in, so the daemon empties the swap as fast as the case fills it.  On
arm64 with 64K pages max_ptes_swap is 1024 pages, which is 64M a step, and
the case loses the race:

    # Swapout 1024 of 8192 pages... Fail
    not ok 10 collapse_max_ptes_swap

Retry for up to two seconds, holding the range out of khugepaged's reach
meanwhile.  The collapse each case runs next restores MADV_HUGEPAGE, so
only the setup is affected.

If the pages still won't swap out, skip: no swap, swap too small or full,
a memcg cap or busy writeback.  None of that is a kernel bug.

Link: https://lore.kernel.org/20260919002451.496763-6-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Assisted-by: LLM
Cc: Alexander Gordeev <agordeev@linux.ibm.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