selftests/vm: add selftest to verify recollapse of THPs

Add selftest specific to madvise collapse context that tests MADV_COLLAPSE
is "successful" if a hugepage-aligned/sized region is already pmd-mapped.

This test also verifies that MADV_COLLAPSE can collapse memory into THPs
even in "madvise" THP mode and the memory isn't marked VM_HUGEPAGE.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Zach O'Keefe <[email protected]>
Cc: Alex Shi <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Chris Kennelly <[email protected]>
Cc: Chris Zankel <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Pavel Begunkov <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Rongwei Wang <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: "Souptick Joarder (HPE)" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: zokeefe

tools/testing/selftests/vm/khugepaged.c

@@ -990,6 +990,36 @@ static void collapse_max_ptes_shared(struct collapse_context *c)
 	munmap(p, hpage_pmd_size);
 }
 
+static void madvise_collapse_existing_thps(void)
+{
+	void *p;
+	int err;
+
+	p = alloc_mapping();
+	fill_memory(p, 0, hpage_pmd_size);
+
+	printf("Collapse fully populated PTE table...");
+	/*
+	 * Note that we don't set MADV_HUGEPAGE here, which
+	 * also tests that VM_HUGEPAGE isn't required for
+	 * MADV_COLLAPSE in "madvise" mode.
+	 */
+	err = madvise(p, hpage_pmd_size, MADV_COLLAPSE);
+	if (err == 0 && check_huge(p)) {
+		success("OK");
+		printf("Re-collapse PMD-mapped hugepage");
+		err = madvise(p, hpage_pmd_size, MADV_COLLAPSE);
+		if (err == 0 && check_huge(p))
+			success("OK");
+		else
+			fail("Fail");
+	} else {
+		fail("Fail");
+	}
+	validate_memory(p, 0, hpage_pmd_size);
+	munmap(p, hpage_pmd_size);
+}
+
 int main(int argc, const char **argv)
 {
 	struct collapse_context c;
@@ -1057,6 +1087,7 @@ int main(int argc, const char **argv)
 		collapse_fork(&c);
 		collapse_fork_compound(&c);
 		collapse_max_ptes_shared(&c);
+		madvise_collapse_existing_thps();
 	}
 
 	restore_settings(0);