drm/i915/selftests: fixup igt_shrink_thp

Since the object might still be active here, the shrink_all will simply
ignore it, which blows up in the test, since the pages will still be
there. Currently THP is disabled which should result in the test being
skipped, but if we ever re-enable THP we might start seeing the failure.
Fix this by forcing I915_SHRINK_ACTIVE.

v2: Some machine in the shard runs doesn't seem to have any available
swap when running this test. Try to handle this.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210906091729.2093312-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/selftests/huge_pages.c

@@ -1519,6 +1519,7 @@ static int igt_shrink_thp(void *arg)
 	struct i915_vma *vma;
 	unsigned int flags = PIN_USER;
 	unsigned int n;
+	bool should_swap;
 	int err = 0;
 
 	/*
@@ -1567,23 +1568,38 @@ static int igt_shrink_thp(void *arg)
 			break;
 	}
 	i915_gem_context_unlock_engines(ctx);
+	/*
+	 * Nuke everything *before* we unpin the pages so we can be reasonably
+	 * sure that when later checking get_nr_swap_pages() that some random
+	 * leftover object doesn't steal the remaining swap space.
+	 */
+	i915_gem_shrink(NULL, i915, -1UL, NULL,
+			I915_SHRINK_BOUND |
+			I915_SHRINK_UNBOUND |
+			I915_SHRINK_ACTIVE);
 	i915_vma_unpin(vma);
 	if (err)
 		goto out_put;
 
 	/*
-	 * Now that the pages are *unpinned* shrink-all should invoke
-	 * shmem to truncate our pages.
+	 * Now that the pages are *unpinned* shrinking should invoke
+	 * shmem to truncate our pages, if we have available swap.
 	 */
-	i915_gem_shrink_all(i915);
-	if (i915_gem_object_has_pages(obj)) {
-		pr_err("shrink-all didn't truncate the pages\n");
+	should_swap = get_nr_swap_pages() > 0;
+	i915_gem_shrink(NULL, i915, -1UL, NULL,
+			I915_SHRINK_BOUND |
+			I915_SHRINK_UNBOUND |
+			I915_SHRINK_ACTIVE);
+	if (should_swap == i915_gem_object_has_pages(obj)) {
+		pr_err("unexpected pages mismatch, should_swap=%s\n",
+		       yesno(should_swap));
 		err = -EINVAL;
 		goto out_put;
 	}
 
-	if (obj->mm.page_sizes.sg || obj->mm.page_sizes.phys) {
-		pr_err("residual page-size bits left\n");
+	if (should_swap == (obj->mm.page_sizes.sg || obj->mm.page_sizes.phys)) {
+		pr_err("unexpected residual page-size bits, should_swap=%s\n",
+		       yesno(should_swap));
 		err = -EINVAL;
 		goto out_put;
 	}