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@xxxxxxxxxx Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Chris Kennelly <ckennelly@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: James Houghton <jthoughton@xxxxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx> Cc: SeongJae Park <sj@xxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Yang Shi <shy828301@xxxxxxxxx> --- tools/testing/selftests/vm/khugepaged.c | 30 +++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/tools/testing/selftests/vm/khugepaged.c b/tools/testing/selftests/vm/khugepaged.c index eabbd2710096..64126c8cd561 100644 --- 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cleanup_area(p, hpage_pmd_size); } +/* + * Test race with khugepaged where page tables have been retracted and + * pmd cleared.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); } -- 2.37.3.998.g577e59143f-goog
