From 665c97150c501d583897152dccc339a161ddf06a Mon Sep 17 00:00:00 2001 From: Zach O'Keefe Date: Thu, 22 Sep 2022 15:40:45 -0700 Subject: [PATCH] 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 Cc: Axel Rasmussen Cc: Chris Kennelly Cc: David Hildenbrand Cc: David Rientjes Cc: Hugh Dickins Cc: James Houghton Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Minchan Kim Cc: Pasha Tatashin Cc: Peter Xu Cc: Rongwei Wang Cc: SeongJae Park Cc: Song Liu Cc: Vlastimil Babka Cc: Yang Shi Signed-off-by: Andrew Morton --- 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 eabbd2710096c..64126c8cd5612 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cleanup_area(p, hpage_pmd_size); } +/* + * Test race with khugepaged where page tables have been retracted and + * pmd cleared.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 [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); } -- 2.39.5