selftests/mm/uffd-stress: stricten constraint on free hugepages needed before the...

The test requires at least 2 * (bytes/page_size) hugetlb memory, since we
require identical number of hugepages for src and dst location.  Fix this.

Along with the above, as explained in patch "selftests/mm/uffd-stress:
Make test operate on less hugetlb memory", the racy nature of the test
requires that we have some extra number of hugepages left beyond what is
required.  Therefore, stricten this constraint.

Link: https://lkml.kernel.org/r/20250909061531.57272-3-dev.jain@arm.com
Fixes: 5a6aa60d1823 ("selftests/mm: skip uffd hugetlb tests with insufficient hugepages")
Signed-off-by: Dev Jain <dev.jain@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index c0f64df5085c4a4cf7928040e8b4febc440af589..ecd016329935a073e7cdd47816664ce44c063076 100644 (file)
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -448,12 +448,6 @@ int main(int argc, char **argv)
        parse_test_type_arg(argv[1]);
        bytes = atol(argv[2]) * 1024 * 1024;
 
-       if (test_type == TEST_HUGETLB &&
-          get_free_hugepages() < bytes / page_size) {
-               printf("skip: Skipping userfaultfd... not enough hugepages\n");
-               return KSFT_SKIP;
-       }
-
        nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
        if (nr_cpus > 32) {
                /* Don't let calculation below go to zero. */
@@ -464,6 +458,17 @@ int main(int argc, char **argv)
                nr_parallel = nr_cpus;
        }
 
+       /*
+        * src and dst each require bytes / page_size number of hugepages.
+        * Ensure nr_parallel - 1 hugepages on top of that to account
+        * for racy extra reservation of hugepages.
+        */
+       if (test_type == TEST_HUGETLB &&
+          get_free_hugepages() < 2 * (bytes / page_size) + nr_parallel - 1) {
+               printf("skip: Skipping userfaultfd... not enough hugepages\n");
+               return KSFT_SKIP;
+       }
+
        nr_pages_per_cpu = bytes / page_size / nr_parallel;
        if (!nr_pages_per_cpu) {
                _err("pages_per_cpu = 0, cannot test (%lu / %lu / %lu)",