selftests/mm: raise the khugepaged test-case cap

Patch series "selftests/mm: improve khugepaged coverage", v6.

khugepaged collapses to mTHP orders since 7.2, and 7.3 added three
selftest cases for it: the generic collapse cases run at one order named
by -c, with the result detected by counting folios of that order.

That leaves the collapse path largely untested.  The suite does not run
where a PMD is 512M.  A folio count cannot say where a collapse landed. 
Fixed sleeps cannot tell "not collapsed" from "not scanned yet".  And
nothing exercises collapse under contention.

Close those gaps in order:

 - Make the suite run at a 512M PMD: scale the collapse wait with the PMD
   size, skip what such a PMD cannot serve, make the swapout the swap
   cases depend on deterministic, and keep khugepaged out of the
   MADV_COLLAPSE cases.

 - Detect results per window rather than by count, with folio-order
   helpers in vm_util that are checked against the kernel before any
   collapse test trusts them.

 - Drive khugepaged deterministically: a completion barrier that wakes the
   daemon and waits for a full pass, and a check that one pass yields one
   attributed collapse.

 - Cover collapse at every supported order by default: which window
   collapses, occupancy at both limits, sources that are already large
   folios, and a fork-shared source under concurrent writes.

 - Race collapse against everything that can touch its sources, at both
   occupancy limits and over whole-table zaps, checked by content and by
   the kernel's own assertions.

Everything passes on an unmodified kernel.


This patch (of 19):

TEST() ends the run with "MAX_TEST_CASES is too small" when the table
fills, and the table holds 64.  A full invocation already registers 63, so
the next case added anywhere aborts the whole suite before a single test
runs.

Raise the cap to 256.  The table is a static array of small structs, so
the room costs nothing worth counting.

Link: https://lore.kernel.org/20260919002451.496763-1-kirill@shutemov.name
Link: https://lore.kernel.org/20260919002451.496763-2-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Usama Arif <usama.arif@linux.dev>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.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: Michal Hocko <mhocko@suse.com>
Cc: Muhammad Usama Anjum <usama.anjum@arm.com>
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: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 525108cace54..c44bc18f7536 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1290,7 +1290,7 @@ struct test_case {
 	test_fn fn;
 };
 
-#define MAX_TEST_CASES 64
+#define MAX_TEST_CASES 256
 static struct test_case test_cases[MAX_TEST_CASES];
 static int nr_test_cases;