memcg_protection.m (2482B)
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