[LTP] [PATCH v3 2/2] memcontrol04: Copy from kselftest

[Michal Koutný]

Hello.

On Tue, Feb 22, 2022 at 12:45:47PM +0000, Richard Palethorpe <rpalethorpe@suse.com> wrote:
> + * "First, this test creates the following hierarchy:
> + * A       memory.low = 50M,  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
> + * A/B/E   memory.low = 500M, memory.current = 0
> + * A/B/F   memory.low = 0,    memory.current = 50M
> + *
> + * Usages are pagecache
> + * Then it creates A/G and creates a significant
> + * memory pressure in it.
> + *
> + * A/B    memory.current ~= 50M
> + * A/B/C  memory.current ~= 33M
> + * A/B/D  memory.current ~= 17M
> + * A/B/E  memory.current ~= 0

This nicely misses the expected consumption of the F cgroup (I see it's
missing in the original too). But one can expect from complementarity
it's zero (if one accepts these values, which unfortunately is not true
with hierarchical & scaled reclaim protection).

> +		if (i < E || (i == F && tst_cg_memory_recursiveprot())) {
> +			TST_EXP_EXPR(low > 0,
> +				     "(%c low events=%ld) > 0", id, low);
> +		} else {
> +			TST_EXP_EXPR(low == 0,
> +				     "(%c low events=%ld) == 0", id, low);
> +		}

Despite this makes the test behavior consistent, I think this is
unexpected behavior with recursive_memoryprot. With the given
configuration, there should never be residual protection that F assumes.

Unless there is a good explanation [1], I'd consider non-zero
memory.events:low in F the test failure here.

Michal

[1] I will need to look into some more detailed tracing data.