[PATCH i-g-t v6 9/9] tests/cgroup_dmem: add write_eviction_nonblock subtest

[Thadeu Lima de Souza Cascardo <cascardo@igalia.com>]

From: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Add write_eviction_nonblock to exercise the O_NONBLOCK path of the dmem
cgroup max interface.  After filling VRAM to the cgroup limit, each
limit-lowering step writes dmem.max with O_NONBLOCK so that synchronous
eviction is skipped.  The test then verifies that usage has not yet
dropped below the new limit, allocates a small BO to trigger eviction
explicitly, and finally confirms that usage falls within bounds.

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
 tests/cgroup_dmem.c | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/tests/cgroup_dmem.c b/tests/cgroup_dmem.c
index 0d3b415acd54..ee6345c17878 100644
--- a/tests/cgroup_dmem.c
+++ b/tests/cgroup_dmem.c
@@ -41,6 +41,7 @@
 #define USAGE_DROP_TIMEOUT_MS	1000
 
 #define TEST_INTERRUPTIBLE	(1 << 0)
+#define TEST_NONBLOCK		(1 << 1)
 
 /**
  * SUBTEST: simple
@@ -90,6 +91,18 @@
  * REQUIREMENTS: must run as root; xe device with at least one VRAM region
  */
 
+/**
+ * SUBTEST: write_eviction_nonblock
+ * DESCRIPTION:
+ *   Same fill phase as write_eviction.  In the limit-lowering phase dmem.max
+ *   is written with O_NONBLOCK, which causes the kernel to skip synchronous
+ *   eviction.  After each nonblock write the test verifies that usage has not
+ *   yet dropped below the new limit, then triggers eviction explicitly by
+ *   allocating a small BO.  Finally verifies that usage falls within bounds
+ *   after the forced eviction.
+ * REQUIREMENTS: must run as root; xe device with at least one VRAM region
+ */
+
 static atomic_int signal_count;
 static struct sigaction sigcont_oldact;
 
@@ -277,7 +290,7 @@ static void test_write_eviction(int fd, char *cg_region, unsigned int flags, con
 	struct igt_cgroup *cg;
 	void **handles;
 	int max_bo;
-	uint64_t current, capacity, cg_max, limit, after;
+	uint64_t current, capacity, cg_max, limit, after, before;
 	int err;
 
 	igt_cgroup_dmem_get_capacity(cg_region, &capacity);
@@ -322,14 +335,31 @@ static void test_write_eviction(int fd, char *cg_region, unsigned int flags, con
 	while (limit >= EVICT_STEP) {
 
 		limit -= EVICT_STEP;
-		igt_cgroup_dmem_set_max(cg, cg_region, limit, false);
+
+		if (flags & TEST_NONBLOCK)
+			igt_cgroup_dmem_get_current(cg, cg_region, &before);
+
+		igt_cgroup_dmem_set_max(cg, cg_region, limit,
+					!!(flags & TEST_NONBLOCK));
 
 		igt_cgroup_dmem_get_current(cg, cg_region, &after);
 		igt_debug("Lowered max to %"PRIu64" MiB: usage = %"PRIu64" MiB\n",
 			  limit / SZ_1M, after / SZ_1M);
 
+		if (flags & TEST_NONBLOCK) {
+			/*
+			 * O_NONBLOCK skips eviction: verify usage has not
+			 * dropped below the new limit yet.
+			 */
+			igt_assert_f(after == before,
+				     "Expected no eviction with O_NONBLOCK, but "
+				     "usage dropped from %"PRIu64" MiB to %"PRIu64" MiB "
+				     "(limit %"PRIu64" MiB)\n",
+				     before / SZ_1M, after / SZ_1M, limit / SZ_1M);
+		}
+
 		if (limit > EVICT_STEP) {
-			if ((flags & TEST_INTERRUPTIBLE) && after > limit) {
+			if ((flags & (TEST_INTERRUPTIBLE | TEST_NONBLOCK)) && after > limit) {
 				/* Let a new bo creation trigger eviction. */
 				void *handle;
 				err = drv->allocate_vram(ctx, BO_SIZE / 8, &handle);
@@ -368,6 +398,7 @@ static const struct {
 	{ "current", test_current, 0 },
 	{ "write_eviction", test_write_eviction, 0 },
 	{ "write_eviction_interruptible", test_write_eviction, TEST_INTERRUPTIBLE },
+	{ "write_eviction_nonblock", test_write_eviction, TEST_NONBLOCK },
 	{ }
 };
 

-- 
2.47.3