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

Michal Koutný
2022-05-13T17:18:10Z

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 Koutn√Ω <mkoutny-IBi9RG/b67k@public.gmane.org>
---
.../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