[LTP] [PATCH] memcg_control_test: Disable swapping in test cgroup for v2

[T.J. Mercier]

memcg_control_test_1 sets both a memory limit and a memsw/swap limit to
a single page, and then asks mem_process to allocate 2 pages in an
attempt to cause a memcg OOM kill. However, if swapping is enabled the
first page can be swapped before the second is allocated causing neither
limit to be exceeded in v2 since there is no combined memsw counter in
v2. In this case no OOM kill will occur which results in a test failure.
Fix this by disabling swap in the test cgroup for v2 if swap is enabled,
causing both pages to always be accounted under the same counter such
that memory.max causes an OOM kill.

Fixes: c0b815736 ("New testcase added by Naufal.")
Signed-off-by: T.J. Mercier <tjmercier@google.com>
---
 .../memcg/control/memcg_control_test.sh            | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/controllers/memcg/control/memcg_control_test.sh b/testcases/kernel/controllers/memcg/control/memcg_control_test.sh
index 68287a70c..79b3a02a9 100644
--- a/testcases/kernel/controllers/memcg/control/memcg_control_test.sh
+++ b/testcases/kernel/controllers/memcg/control/memcg_control_test.sh
@@ -12,7 +12,6 @@ TST_NEEDS_TMPDIR=1
 
 PAGE_SIZE=$(tst_getconf PAGESIZE)
 
-TOT_MEM_LIMIT=$PAGE_SIZE
 ACTIVE_MEM_LIMIT=$PAGE_SIZE
 PROC_MEM=$((PAGE_SIZE * 2))
 
@@ -50,13 +49,22 @@ test1()
 
 	# If the kernel is built without swap, the $memsw_memory_limit file is missing
 	if [ -e "$test_dir/$memsw_memory_limit" ]; then
-		ROD echo "$TOT_MEM_LIMIT" \> "$test_dir/$memsw_memory_limit"
+		if [ "$cgroup_version" = "2" ]; then
+			# v2 does not have a combined memsw limit like v1.
+			# Disable swapping in v2 so all pages get acccounted to the non-swap counter.
+			SWAP_LIMIT=0
+		else
+			# Swapping cannot be disabled via memsw.limit_in_bytes in v1.
+			# Apply a memsw limit in v1 to capture any swapped pages
+			SWAP_LIMIT=$ACTIVE_MEM_LIMIT
+		fi
+		ROD echo "$SWAP_LIMIT" \> "$test_dir/$memsw_memory_limit"
 	fi
 
 	KILLED_CNT=0
 	test_proc_kill
 
-	if [ $PROC_MEM -gt $TOT_MEM_LIMIT ] && [ $KILLED_CNT -eq 0 ]; then
+	if [ $KILLED_CNT -eq 0 ]; then
 		tst_res TFAIL "Test #1: failed"
 	else
 		tst_res TPASS "Test #1: passed"
-- 
2.49.0.472.ge94155a9ec-goog