cgroup: account for memory_recursiveprot in test_memcg_low()

The test_memcg_low() testcase in test_memcontrol.c verifies the expected
behavior of groups using the memory.low knob.  Part of the testcase
verifies that a group with memory.low that experiences reclaim due to
memory pressure elsewhere in the system, observes memory.events.low events
as a result of that reclaim.

In commit 8a931f801340 ("mm: memcontrol: recursive memory.low
protection"), the memory controller was updated to propagate memory.low
and memory.min protection from a parent group to its children via a
configurable memory_recursiveprot mount option.  This unfortunately broke
the memcg tests, which asserts that a sibling that experienced reclaim but
had a memory.low value of 0, would not observe any memory.low events.
This patch updates test_memcg_low() to account for the new behavior
introduced by memory_recursiveprot.

So as to make the test resilient to multiple configurations, the patch
also adds a new proc_mount_contains() helper that checks for a string in
/proc/mounts, and is used to toggle behavior based on whether the default
memory_recursiveprot was present.

Link: https://lkml.kernel.org/r/20220423155619.3669555-3-void@manifault.com
Signed-off-by: David Vernet <void@manifault.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
index e6f3679..b4d7027 100644 (file)
--- a/tools/testing/selftests/cgroup/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/cgroup_util.c
@@ -528,6 +528,18 @@ int set_oom_adj_score(int pid, int score)
        return 0;
 }
 
+int proc_mount_contains(const char *option)
+{
+       char buf[4 * PAGE_SIZE];
+       ssize_t read;
+
+       read = read_text("/proc/mounts", buf, sizeof(buf));
+       if (read < 0)
+               return read;
+
+       return strstr(buf, option) != NULL;
+}
+
 ssize_t proc_read_text(int pid, bool thread, const char *item, char *buf, size_t size)
 {
        char path[PATH_MAX];

diff --git a/tools/testing/selftests/cgroup/cgroup_util.h b/tools/testing/selftests/cgroup/cgroup_util.h
index 6287385..756f760 100644 (file)
--- a/tools/testing/selftests/cgroup/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/cgroup_util.h
@@ -48,6 +48,7 @@ extern int is_swap_enabled(void);
 extern int set_oom_adj_score(int pid, int score);
 extern int cg_wait_for_proc_count(const char *cgroup, int count);
 extern int cg_killall(const char *cgroup);
+int proc_mount_contains(const char *option);
 extern ssize_t proc_read_text(int pid, bool thread, const char *item, char *buf, size_t size);
 extern int proc_read_strstr(int pid, bool thread, const char *item, const char *needle);
 extern pid_t clone_into_cgroup(int cgroup_fd);

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index d240a39..4da138d 100644 (file)
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -21,6 +21,8 @@
 #include "../kselftest.h"
 #include "cgroup_util.h"
 
+static bool has_recursiveprot;
+
 /*
  * This test creates two nested cgroups with and without enabling
  * the memory controller.
@@ -525,15 +527,18 @@ static int test_memcg_low(const char *root)
        }
 
        for (i = 0; i < ARRAY_SIZE(children); i++) {
+               int no_low_events_index = has_recursiveprot ? 2 : 1;
+
                oom = cg_read_key_long(children[i], "memory.events", "oom ");
                low = cg_read_key_long(children[i], "memory.events", "low ");
 
                if (oom)
                        goto cleanup;
-               if (i < 2 && low <= 0)
+               if (i <= no_low_events_index && low <= 0)
                        goto cleanup;
-               if (i >= 2 && low)
+               if (i > no_low_events_index && low)
                        goto cleanup;
+
        }
 
        ret = KSFT_PASS;
@@ -1382,7 +1387,7 @@ struct memcg_test {
 int main(int argc, char **argv)
 {
        char root[PATH_MAX];
-       int i, ret = EXIT_SUCCESS;
+       int i, proc_status, ret = EXIT_SUCCESS;
 
        if (cg_find_unified_root(root, sizeof(root)))
                ksft_exit_skip("cgroup v2 isn't mounted\n");
@@ -1398,6 +1403,11 @@ int main(int argc, char **argv)
                if (cg_write(root, "cgroup.subtree_control", "+memory"))
                        ksft_exit_skip("Failed to set memory controller\n");
 
+       proc_status = proc_mount_contains("memory_recursiveprot");
+       if (proc_status < 0)
+               ksft_exit_skip("Failed to query cgroup mount option\n");
+       has_recursiveprot = proc_status;
+
        for (i = 0; i < ARRAY_SIZE(tests); i++) {
                switch (tests[i].fn(root)) {
                case KSFT_PASS: