[LTP] [PATCH 2/2] memcg/memcontrol0[34]: Remove protection from the top level group

[Wei Gao]

On Sat, Sep 26, 2026 at 10:44:54PM +0200, Sebastian Chlad wrote:
> From: Sebastian Chlad <sebastian.chlad@suse.com>
> 
> The memory pressure in both tests comes from A/G hitting the
> memory.max of A, so A is the reclaim root. Protection of the reclaim
> root is ignored by the kernel and the direct children of the root
> (A/B and A/G) use their own memory.min/memory.low as is, see
> page_counter_calculate_protection(). The 50M of memory.min
> (memcontrol03) and memory.low (memcontrol04) set on A thus has no
> effect on what the tests check; it would only protect the whole
> hierarchy against reclaim from outside, which the tests don't need.
> 
> The kselftest the tests are ported from dropped it for the same reason
> in kernel commit 6a35919005d4 ("selftests: memcg: remove protection
> from top level memcg"). Do the same and correct the descriptions, as
> the pressure is created in A, not in A/G.
> 
> Signed-off-by: Sebastian Chlad <sebastian.chlad@suse.com>
> ---
>  testcases/kernel/controllers/memcg/memcontrol03.c | 5 ++---
>  testcases/kernel/controllers/memcg/memcontrol04.c | 5 ++---
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/testcases/kernel/controllers/memcg/memcontrol03.c b/testcases/kernel/controllers/memcg/memcontrol03.c
> index aa94f4999..25b84c24e 100644
> --- a/testcases/kernel/controllers/memcg/memcontrol03.c
> +++ b/testcases/kernel/controllers/memcg/memcontrol03.c
> @@ -5,7 +5,7 @@
>   *
>   * Original description:
>   * "First, this test creates the following hierarchy:
> - * A       memory.min = 50M,  memory.max = 200M
> + * A       memory.min = 0,    memory.max = 200M
>   * A/B     memory.min = 50M,  memory.current = 50M
>   * A/B/C   memory.min = 75M,  memory.current = 50M
>   * A/B/D   memory.min = 25M,  memory.current = 50M
> @@ -15,7 +15,7 @@
>   * Usages are pagecache, but the test keeps a running
>   * process in every leaf cgroup.
>   * Then it creates A/G and creates a significant
> - * memory pressure in it.
> + * memory pressure in A.
>   *
>   * A/B    memory.current ~= 50M
>   * A/B/C  memory.current ~= 29M
> @@ -194,7 +194,6 @@ static void test_memcg_min(void)
>  		alloc_pagecache_in_child(leaf_cg[i], MB(50));
>  	}
>  
> -	SAFE_CG_PRINT(trunk_cg[A], "memory.min", "50M");
>  	SAFE_CG_PRINT(trunk_cg[B], "memory.min", "50M");
>  	SAFE_CG_PRINT(leaf_cg[C], "memory.min", "75M");
>  	SAFE_CG_PRINT(leaf_cg[D], "memory.min", "25M");
> diff --git a/testcases/kernel/controllers/memcg/memcontrol04.c b/testcases/kernel/controllers/memcg/memcontrol04.c
> index 92ab53a51..f1e136df4 100644
> --- a/testcases/kernel/controllers/memcg/memcontrol04.c
> +++ b/testcases/kernel/controllers/memcg/memcontrol04.c
> @@ -5,7 +5,7 @@
>   *
>   * Original description:
>   * "First, this test creates the following hierarchy:
> - * A       memory.low = 50M,  memory.max = 200M
> + * A       memory.low = 0,    memory.max = 200M
>   * A/B     memory.low = 50M,  memory.current = 50M
>   * A/B/C   memory.low = 75M,  memory.current = 50M
>   * A/B/D   memory.low = 25M,  memory.current = 50M
> @@ -14,7 +14,7 @@
>   *
>   * Usages are pagecache
>   * Then it creates A/G and creates a significant
> - * memory pressure in it.
> + * memory pressure in A.
>   *
>   * A/B    memory.current ~= 50M
>   * A/B/C  memory.current ~= 29M
> @@ -167,7 +167,6 @@ static void test_memcg_low(void)
>  		alloc_pagecache_in_child(leaf_cg[i], MB(50));
>  	}
>  
> -	SAFE_CG_PRINT(trunk_cg[A], "memory.low", "50M");
>  	SAFE_CG_PRINT(trunk_cg[B], "memory.low", "50M");
>  	SAFE_CG_PRINT(leaf_cg[C], "memory.low", "75M");
>  	SAFE_CG_PRINT(leaf_cg[D], "memory.low", "25M");
> -- 
> 2.51.0
Reviewed-by: Wei Gao <wegao@suse.com>

> 
> 
> -- 
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