[PATCH 3/4] selftests: memcg: Adjust expected reclaim values of protected cgroups

[Michal Koutný <mkoutny@xxxxxxxx>]

The numbers are not easy to derive in a closed form (certainly mere
protections ratios do not apply), therefore use a simulation to obtain
expected numbers.

The new values make the protection tests succeed more precisely.

	% run as: octave-cli script
	%
	% Input configurations
	% -------------------
	% E parent effective protection
	% n nominal protection of siblings set at the givel level
	% c current consumption -,,-

	% example from testcase (values in GB)
	E = 50 / 1024;
	n = [75 25 0 500 ] / 1024;
	c = [50 50 50 0] / 1024;

	% Reclaim parameters
	% ------------------

	% Minimal reclaim amount (GB)
	cluster = 32*4 / 2**20;

	% Reclaim coefficient (think as 0.5^sc->priority)
	alpha = .1

	% Simulation parameters
	% ---------------------
	epsilon = 1e-7;
	timeout = 1000;

	% Simulation loop
	% ---------------------
	% Simulation assumes siblings consumed the initial amount of memory (w/out
	% reclaim) and then the reclaim starts, all memory is reclaimable, i.e. treated
	% same. It simulates only non-low reclaim and assumes all memory.min = 0.

	ch = [];
	eh = [];
	rh = [];

	for t = 1:timeout
		% low_usage
		u = min(c, n);
		siblings = sum(u);

		% effective_protection()
		protected = min(n, c);                % start with nominal
		e = protected * min(1, E / siblings); % normalize overcommit

		% recursive protection
		unclaimed = max(0, E - siblings);
		parent_overuse = sum(c) - siblings;
		if (unclaimed > 0 && parent_overuse > 0)
			overuse = max(0, c - protected);
			e += unclaimed * (overuse / parent_overuse);
		endif

		% get_scan_count()
		r = alpha * c;             % assume all memory is in a single LRU list

		% commit 1bc63fb1272b ("mm, memcg: make scan aggression always exclude protection")
		sz = max(e, c);
		r .*= (1 - (e+epsilon) ./ (sz+epsilon));

		% uncomment to debug prints
		% e, c, r

		% nothing to reclaim, reached equilibrium
		if max(r) < epsilon
			break;
		endif

		% SWAP_CLUSTER_MAX
		r = max(r, (r > epsilon) .* cluster);
		% XXX here I do parallel reclaim of all siblings
		% in reality reclaim is serialized and each sibling recalculates own residual
		c = max(c - r, 0);

		ch = [ch ; c];
		eh = [eh ; e];
		rh = [rh ; r];
	endfor

	t
	c, e

Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
---
 .../selftests/cgroup/test_memcontrol.c        | 20 +++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index eba252fa64ac..9ffacf024bbd 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -260,9 +260,9 @@ static int cg_test_proc_killed(const char *cgroup)
  * memory pressure in it.
  *
  * A/B    memory.current ~= 50M
- * A/B/C  memory.current ~= 33M
- * A/B/D  memory.current ~= 17M
- * A/B/F  memory.current ~= 0
+ * A/B/C  memory.current ~= 29M
+ * A/B/D  memory.current ~= 21M
+ * A/B/E  memory.current ~= 0
  *
  * After that it tries to allocate more than there is
  * unprotected memory in A available, and checks
@@ -365,10 +365,10 @@ static int test_memcg_min(const char *root)
 	for (i = 0; i < ARRAY_SIZE(children); i++)
 		c[i] = cg_read_long(children[i], "memory.current");
 
-	if (!values_close(c[0], MB(33), 10))
+	if (!values_close(c[0], MB(29), 10))
 		goto cleanup;
 
-	if (!values_close(c[1], MB(17), 10))
+	if (!values_close(c[1], MB(21), 10))
 		goto cleanup;
 
 	if (c[3] != 0)
@@ -417,9 +417,9 @@ static int test_memcg_min(const char *root)
  *
  * Then it checks actual memory usages and expects that:
  * A/B    memory.current ~= 50M
- * A/B/   memory.current ~= 33M
- * A/B/D  memory.current ~= 17M
- * A/B/F  memory.current ~= 0
+ * A/B/   memory.current ~= 29M
+ * A/B/D  memory.current ~= 21M
+ * A/B/E  memory.current ~= 0
  *
  * After that it tries to allocate more than there is
  * unprotected memory in A available,
@@ -512,10 +512,10 @@ static int test_memcg_low(const char *root)
 	for (i = 0; i < ARRAY_SIZE(children); i++)
 		c[i] = cg_read_long(children[i], "memory.current");
 
-	if (!values_close(c[0], MB(33), 10))
+	if (!values_close(c[0], MB(29), 10))
 		goto cleanup;
 
-	if (!values_close(c[1], MB(17), 10))
+	if (!values_close(c[1], MB(21), 10))
 		goto cleanup;
 
 	if (c[3] != 0)
-- 
2.35.3