[LTP] [RFC PATCH 4/4] memcg_stress_test.sh: allocate less than CommitLimit bytes

[Stanislav Kholmanskikh]

If we run this test case on a system, where the amount of
physical RAM is significantly more than the amount of swap
space (for example, 128G vs 1G), one of the memcg_process_stress
processes will invoke the OOM-killer, and the test will fail
(in the least bad case).

The key here is to find out a more generic formula instead of

mem=$(( $mem_free + $swap_free / 2 ))

Per my understanding, this test case does not require all the
memory of the system.

Given that, (CommitLimit - Committed_AS) with overcommit_memory == 1,
looks to be a suitable formula, since the kernel lets allocate this
amount of memory and there will be some memory for other tasks.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
---
 .../controllers/memcg/stress/memcg_stress_test.sh  |   28 ++++++++++++++++---
 1 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh b/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
index 0d541e5..75baab4 100755
--- a/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
+++ b/testcases/kernel/controllers/memcg/stress/memcg_stress_test.sh
@@ -39,6 +39,8 @@ children=""
 nr_children=0
 memcg_path=/dev/memcg
 memcg_created=0
+overcommit_path=/proc/sys/vm/overcommit_memory
+overcommit=""
 
 cleanup()
 {
@@ -54,6 +56,10 @@ cleanup()
 		umount "$memcg_path"
 		rmdir "$memcg_path"
 	fi
+
+	if is_int "$overcommit"; then
+		echo "$overcommit" > "$overcommit_path"
+	fi
 }
 TST_CLEANUP=cleanup
 
@@ -139,20 +145,32 @@ testcase_2()
 ROD echo 3 \> /proc/sys/vm/drop_caches
 sleep 2
 
-mem_free=`cat /proc/meminfo | grep MemFree | awk '{ print $2 }'`
-is_int "$mem_free" || tst_brkm TBROK "Unable to determine mem_free"
+# We enable the "always overcommit" memory policy and allocate
+# less than CommitLimit bytes. Given that no other memory-consuming
+# process should be running, this gives us a more-or-less strong
+# guarantee that our allocations will result in an OOM situation.
+
+overcommit=$(cat "$overcommit_path")
+is_int "$overcommit" || tst_brkm TBROK "Unable to determine overcommit"
 
-swap_free=`cat /proc/meminfo | grep SwapFree | awk '{ print $2 }'`
-is_int "$swap_free" || tst_brkm TBROK "Unable to determine swap_free"
+commit_limit=$(cat /proc/meminfo | grep CommitLimit | awk '{ print $2 }')
+is_int "$commit_limit" || tst_brkm TBROK "Unable to determine commit_limit"
 
-mem=$(( $mem_free + $swap_free / 2 ))
+committed_as=$(cat /proc/meminfo | grep Committed_AS | awk '{ print $2 }')
+is_int "$committed_as" || tst_brkm TBROK "Unable to determine committed_as"
+
+mem=$(( $commit_limit - $committed_as ))
 mem=$(( $mem / 1024 ))
 [ "$mem" -gt 0 ] || tst_brkm TBROK "mem is negative: $mem"
 
+ROD echo 1 \> "$overcommit_path"
+
 date
 testcase_1
 date
 testcase_2
 date
 
+ROD echo "$overcommit" \> "$overcommit_path"
+
 tst_exit
-- 
1.7.1