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)
20 E = 50 / 1024;
21 n = [75 25 0 500 ] / 1024;
22 c = [50 50 50 0] / 1024;
23
24 % Reclaim parameters
25 % ------------------
26
27 % Minimal reclaim amount (GB)
28 cluster = 32*4 / 2**20;
29
30 % Reclaim coefficient (think as 0.5^sc->priority)
31 alpha = .1
32
33 % Simulation parameters
34 % ---------------------
35 epsilon = 1e-7;
36 timeout = 1000;
37
38 % Simulation loop
39 % ---------------
40
41 ch = [];
42 eh = [];
43 rh = [];
44
45 for 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];
86 endfor
87
88 t
89 c, e
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