selftests/vm: add file/shmem MADV_COLLAPSE selftest for cleared pmd

This test tests that MADV_COLLAPSE acting on file/shmem memory for which
(1) the file extent mapping by the memory is already a huge page in the
page cache, and (2) the pmd mapping this memory in the target process is
none.

In practice, (1)+(2) is the state left over after khugepaged has
successfully collapsed file/shmem memory for a target VMA, but the memory
has not yet been refaulted.  So, this test in-effect tests MADV_COLLAPSE
racing with khugepaged to collapse the memory first.

Link: https://lkml.kernel.org/r/20220907144521.3115321-10-zokeefe@google.com
Link: https://lkml.kernel.org/r/20220922224046.1143204-10-zokeefe@google.com
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/vm/khugepaged.c b/tools/testing/selftests/vm/khugepaged.c
index eabbd27..64126c8 100644 (file)
--- a/tools/testing/selftests/vm/khugepaged.c
+++ b/tools/testing/selftests/vm/khugepaged.c
@@ -1353,6 +1353,33 @@ static void madvise_collapse_existing_thps(struct collapse_context *c,
        ops->cleanup_area(p, hpage_pmd_size);
 }
 
+/*
+ * Test race with khugepaged where page tables have been retracted and
+ * pmd cleared.
+ */
+static void madvise_retracted_page_tables(struct collapse_context *c,
+                                         struct mem_ops *ops)
+{
+       void *p;
+       int nr_hpages = 1;
+       unsigned long size = nr_hpages * hpage_pmd_size;
+
+       p = ops->setup_area(nr_hpages);
+       ops->fault(p, 0, size);
+
+       /* Let khugepaged collapse and leave pmd cleared */
+       if (wait_for_scan("Collapse and leave PMD cleared", p, nr_hpages,
+                         ops)) {
+               fail("Timeout");
+               return;
+       }
+       success("OK");
+       c->collapse("Install huge PMD from page cache", p, nr_hpages, ops,
+                   true);
+       validate_memory(p, 0, size);
+       ops->cleanup_area(p, size);
+}
+
 static void usage(void)
 {
        fprintf(stderr, "\nUsage: ./khugepaged <test type> [dir]\n\n");
@@ -1524,5 +1551,8 @@ int main(int argc, const char **argv)
        TEST(madvise_collapse_existing_thps, madvise_context, file_ops);
        TEST(madvise_collapse_existing_thps, madvise_context, shmem_ops);
 
+       TEST(madvise_retracted_page_tables, madvise_context, file_ops);
+       TEST(madvise_retracted_page_tables, madvise_context, shmem_ops);
+
        restore_settings(0);
 }