linux-kernel - Re: [PATCH 3/5] cgroup: Account for memory_localevents in test_memcg_oom_group_leaf

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Date:   Fri, 22 Apr 2022 16:14:49 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     David Vernet <void@...ifault.com>
Cc:     akpm@...ux-foundation.org, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org, hannes@...xchg.org, mhocko@...nel.org,
        shakeelb@...gle.com, kernel-team@...com
Subject: Re: [PATCH 3/5] cgroup: Account for memory_localevents in
 test_memcg_oom_group_leaf_events()

On Fri, Apr 22, 2022 at 08:57:27AM -0700, David Vernet wrote:
> The test_memcg_oom_group_leaf_events() testcase in the cgroup memcg tests
> validates that processes in a group that perform allocations exceeding
> memory.oom.group are killed. It also validates that the
> memory.events.oom_kill events are properly propagated in this case.  Commit
> 06e11c907ea4 ("kselftests: memcg: update the oom group leaf events test")
> fixed test_memcg_oom_group_leaf_events() to account for the fact that the
> memory.events.oom_kill events in a child cgroup is propagated up to its
> parent. This behavior can actually be configured by the memory_localevents
> mount option, so this patch updates the testcase to properly account for
> the possible presence of this mount option.
> 
> Signed-off-by: David Vernet <void@...ifault.com>
> ---
>  .../testing/selftests/cgroup/test_memcontrol.c  | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> index ea2fd27e52df..d88e0ca3f3d1 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> @@ -21,6 +21,7 @@
>  #include "../kselftest.h"
>  #include "cgroup_util.h"
>  
> +static bool has_localevents;
>  static bool has_recursiveprot;
>  
>  /*
> @@ -1091,6 +1092,7 @@ static int test_memcg_oom_group_leaf_events(const char *root)
>  {
>  	int ret = KSFT_FAIL;
>  	char *parent, *child;
> +	long parent_oom_events;
>  
>  	parent = cg_name(root, "memcg_test_0");
>  	child = cg_name(root, "memcg_test_0/memcg_test_1");
> @@ -1128,7 +1130,15 @@ static int test_memcg_oom_group_leaf_events(const char *root)
>  	if (cg_read_key_long(child, "memory.events", "oom_kill ") <= 0)
>  		goto cleanup;
>  
> -	if (cg_read_key_long(parent, "memory.events", "oom_kill ") <= 0)
> +	parent_oom_events = cg_read_key_long(
> +			parent, "memory.events", "oom_kill ");
> +	// If memory_localevents is not enabled (the default), the parent should
> +	// count OOM events in its children groups. Otherwise, it should not
> +	// have observed any events.

Please, use /* */ style comments, it's a generic kernel style.

> +	if (has_localevents) {
> +		if (parent_oom_events != 0)
> +			goto cleanup;
> +	} else if (parent_oom_events <= 0)
>  		goto cleanup;

How about something like this? IMO a bit more clear what's going on.
	if ((has_local_events && parent_oom_events == 0) ||
	    parent_oom_events > 0)
		ret = KSFT_PASS;

Anyway, looks good to me.
Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>

>  
>  	ret = KSFT_PASS;
> @@ -1298,6 +1308,11 @@ int main(int argc, char **argv)
>  		ksft_exit_skip("Failed to query cgroup mount option\n");
>  	has_recursiveprot = proc_status;
>  
> +	proc_status = proc_mount_contains("memory_localevents");
> +	if (proc_status < 0)
> +		ksft_exit_skip("Failed to query cgroup mount option\n");
> +	has_localevents = proc_status;
> +
>  	for (i = 0; i < ARRAY_SIZE(tests); i++) {
>  		switch (tests[i].fn(root)) {
>  		case KSFT_PASS:
> -- 
> 2.30.2
>