1% SPDX-License-Identifier: GPL-2.0
2%
3% run as: octave-cli memcg_protection.m
4%
5% This script simulates reclaim protection behavior on a single level of memcg
6% hierarchy to illustrate how overcommitted protection spreads among siblings
7% (as it depends also on their current consumption).
8%
9% Simulation assumes siblings consumed the initial amount of memory (w/out
10% reclaim) and then the reclaim starts, all memory is reclaimable, i.e. treated
11% same. It simulates only non-low reclaim and assumes all memory.min = 0.
12%
13% Input configurations
14% --------------------
15% E number	parent effective protection
16% n vector	nominal protection of siblings set at the given level (memory.low)
17% c vector	current consumption -,,- (memory.current)
18
19% example from testcase (values in GB)
20E = 50 / 1024;
21n = [75 25 0 500 ] / 1024;
22c = [50 50 50 0] / 1024;
23
24% Reclaim parameters
25% ------------------
26
27% Minimal reclaim amount (GB)
28cluster = 32*4 / 2**20;
29
30% Reclaim coefficient (think as 0.5^sc->priority)
31alpha = .1
32
33% Simulation parameters
34% ---------------------
35epsilon = 1e-7;
36timeout = 1000;
37
38% Simulation loop
39% ---------------
40
41ch = [];
42eh = [];
43rh = [];
44
45for t = 1:timeout
46        % low_usage
47        u = min(c, n);
48        siblings = sum(u);
49
50        % effective_protection()
51        protected = min(n, c);                % start with nominal
52        e = protected * min(1, E / siblings); % normalize overcommit
53
54        % recursive protection
55        unclaimed = max(0, E - siblings);
56        parent_overuse = sum(c) - siblings;
57        if (unclaimed > 0 && parent_overuse > 0)
58                overuse = max(0, c - protected);
59                e += unclaimed * (overuse / parent_overuse);
60        endif
61
62        % get_scan_count()
63        r = alpha * c;             % assume all memory is in a single LRU list
64
65        % commit 1bc63fb1272b ("mm, memcg: make scan aggression always exclude protection")
66        sz = max(e, c);
67        r .*= (1 - (e+epsilon) ./ (sz+epsilon));
68
69        % uncomment to debug prints
70        % e, c, r
71
72        % nothing to reclaim, reached equilibrium
73        if max(r) < epsilon
74                break;
75        endif
76
77        % SWAP_CLUSTER_MAX roundup
78        r = max(r, (r > epsilon) .* cluster);
79        % XXX here I do parallel reclaim of all siblings
80        % in reality reclaim is serialized and each sibling recalculates own residual
81        c = max(c - r, 0);
82
83        ch = [ch ; c];
84        eh = [eh ; e];
85        rh = [rh ; r];
86endfor
87
88t
89c, e
90