Lines Matching +full:feedback +full:- +full:loop

1 .. SPDX-License-Identifier: GPL-2.0
4 Multi-Gen LRU
6 The multi-gen LRU is an alternative LRU implementation that optimizes
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20 * Simple self-correcting heuristics
23 implementations. In the multi-gen LRU, each generation represents a
25 (time-based) common frame of reference and therefore help make better
41 choices; thus self-correction is necessary.
43 The benefits of simple self-correcting heuristics are self-evident.
46 categorized based on additional factors, and a feedback loop can
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84 ``lrugen->max_seq`` for both anon and file types as they are aged on
86 ``lrugen->min_seq[]`` separately for anon and file types as clean file
91 bits in order to fit into the gen counter in ``folio->flags``. Each
92 truncated generation number is an index to ``lrugen->folios[]``. The
96 ``lrugen->folios[]``; otherwise it stores zero.
100 generations, tiers do not have dedicated ``lrugen->folios[]``. In
103 ``folio->flags`` and therefore has a negligible cost. A feedback loop
110 eviction. They form a closed-loop system, i.e., the page reclaim.
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115 increments ``max_seq`` when ``max_seq-min_seq+1`` approaches
120 young PTEs. For the former, it iterates ``lruvec_memcg()->mm_list``
129 --------
131 increments ``min_seq`` when ``lrugen->folios[]`` indexed by
135 a lower refault percentage. The first tier contains single-use
140 was accessed multiple times through file descriptors and the feedback
141 loop has detected outlying refaults from the tier this page is in. To
142 this end, the feedback loop uses the first tier as the baseline, for
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154 This time-based approach has the following advantages:
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166 A page table walker iterates ``lruvec_memcg()->mm_list`` and calls
181 Rmap/PT walk feedback
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193 forms a feedback loop between the eviction and the aging.
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212 --------------
213 A feedback loop modeled after the Proportional-Integral-Derivative
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225 An memcg LRU is a per-node LRU of memcgs. It is also an LRU of LRUs,
228 global reclaim, which is critical to system-wide memory overcommit in
249 best-case complexity from O(n) to O(1) and does not affect the
250 worst-case complexity O(n). Therefore, on average, it has a sublinear
254 -------
255 The multi-gen LRU (of folios) can be disassembled into the following
261 * Bloom filters for rmap/PT walk feedback
262 * PID controller for refault feedback
264 The aging and the eviction form a producer-consumer model;
268 Within the eviction, the PID controller uses refaults as the feedback