linux-kernel - Re: [PATCH v4 1/2] mm/vmscan: Skip memcg with !usage in shrink_node

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Message-ID: <awgbdn6gwnj4kfaezsorvopgsdyoty3yahdeanqvoxstz2w2ke@xc3sv43elkz5>
Date: Mon, 7 Apr 2025 17:25:15 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Waiman Long <longman@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Tejun Heo <tj@...nel.org>, Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 1/2] mm/vmscan: Skip memcg with !usage in
 shrink_node_memcgs()

Hi Waiman.

On Sun, Apr 06, 2025 at 09:41:58PM -0400, Waiman Long <longman@...hat.com> wrote:
 ...
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> index 16f5d74ae762..bab826b6b7b0 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c

I'd suggest updating also the header of the test for clarity and then
exempt the Child 2 ('E') conditionally from comparisons, something like:

@@ -380,10 +380,10 @@ static bool reclaim_until(const char *memcg, long goal);
  *
  * Then it checks actual memory usages and expects that:
  * A/B    memory.current ~= 50M
- * A/B/C  memory.current ~= 29M
- * A/B/D  memory.current ~= 21M
- * A/B/E  memory.current ~= 0
- * A/B/F  memory.current  = 0
+ * A/B/C  memory.current ~= 29M, memory.events:low > 0
+ * A/B/D  memory.current ~= 21M, memory.events:low > 0
+ * A/B/E  memory.current ~= 0,   memory.events:low not specified (==0 w/out memory_recursiveprot)
+ * A/B/F  memory.current  = 0,   memory.events:low == 0
  * (for origin of the numbers, see model in memcg_protection.m.)
  *
  * After that it tries to allocate more than there is
@@ -527,6 +527,7 @@ static int test_memcg_protection(const char *root, bool min)

        for (i = 0; i < ARRAY_SIZE(children); i++) {
                int no_low_events_index = 1;
+               int ignore_low_events_index = has_recursiveprot ? 2 : -1;
                long low, oom;

                oom = cg_read_key_long(children[i], "memory.events", "oom ");
@@ -534,6 +535,8 @@ static int test_memcg_protection(const char *root, bool min)

                if (oom)
                        goto cleanup;
+               if (i == ignore_low_events_index)
+                       continue;
                if (i <= no_low_events_index && low <= 0)
                        goto cleanup;
                if (i > no_low_events_index && low)

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